/Learn-Python-3

Python 3 - Notes based on the Python 3 Essential Training

Primary LanguageJupyter Notebook

Python 3 Notes and Snippets

Table of Contents (chapters)

4. General Syntax

__main__ is the name of the scope in which top-level code executes. A module’s __name__ is set equal to __main__ when read from standard input, a script, or from an interactive prompt.

A module can discover whether or not it is running in the main scope by checking its own __name__, which allows a common idiom for conditionally executing code in a module when it is run as a script or with python -m but not when it is imported:

if __name__ == "__main__":
    # execute only if run as a script
    main()

This is how we can call the main() function when script is executed and a chain of function execution occurs:

def main():
    #call function add
    add()

def add():
    #call function printOut
    printOut()

def printOut():
    print("Hello World")

if __name__ == "__main__": main()
def main():
    #call function add
    add()

def add():
    #call function printOut
    printOut()

def printOut():
    print("Hello World")

if __name__ == "__main__": main()
Hello World

If we didn't have a main() function defined we wont be able to run functions that are defined afterwards. See example:

We are calling egg() function from within main() though it is defined afterwards.

def main():
    print("This is the main function")
    egg()

def egg():
    print('egg')

if __name__ == "__main__": main()
This is the main function
egg

Note:

  • If we didn't have a main() function we would get an error as shown below because we can't call egg() before it's defined
  • Using main() function allows us to control the order of the functions we can to call/run on execution
# del easterEgg
try:
    easterEgg()
except:
    print('ERROR: easterEgg is not defined')

def easterEgg():
    print('egg')
ERROR: easterEgg is not defined

Assigning Values

# Assign multiple variables

firstName, lastName, homeCity = 'James', 'Bond', 'Kansas City'

print('{} {} is from {}'.format(firstName, lastName, homeCity))
James Bond is from Kansas City

subject, grade = "Math", 98

print("He got {} in {}".format(grade, subject))
He got 98 in Math

Making copies of variables

## making copy of varibales 
val_one = 1200
val_two = val_one
#if I change val_one it would not impact val_two
val_one = 1150

print('value one = {} and value two changes to = {}\n'.format(val_one, val_two))
print('memory address for val_one = {} \nmemory address for val_two = {}\n'.format(id(val_one), id(val_two)))

## making a copy of lists the wrong way (both pointing to the same memory address)
list_one = [1,2,3,4,5]
list_two = list_one
list_one.remove(2)

print('first list = {} and second list changes to = {}\n'.format(list_one, list_two))
print('memory address for val_one = {} \nmemory address for val_two = {}'.format(id(list_one), id(list_two)))
value one = 1150 and value two changes to = 1200

memory address for val_one = 4563873264 
memory address for val_two = 4563873392

first list = [1, 3, 4, 5] and second list changes to = [1, 3, 4, 5]

memory address for val_one = 4563366728 
memory address for val_two = 4563366728

Example using Python for Swapping Values

a, b = "A", "B"
a, b = b, a
print(a)
print(b)
B
A

Printing in Python

# print strings or numbers simple example
print(1)
print("hello world")
print(1+2+2)
1
hello world
5

#print variables
a = "Hello World"
b = 1
c = 1+2+3

print(a)
print(b)
print(c)
Hello World
1
6

Printing using .format()

#Print examples using text and variables via Format
score1 = 100
score2 = 95

print("My score in math was {} and in physics was {}".format(score1, score2))
My score in math was 100 and in physics was 95

Printing memory address

score3 = 80
id(score3)
4527044016

#using print() function
varA = 100

print("varA has a value = {} and a memory address = {}".format(varA, id(varA)))
varA has a value = 100 and a memory address = 4527044656

Conditional Assignment

def main():
    a, b = 0, 1
    s = "less than" if a < b else "not less than"
    print(s)

if __name__ == "__main__": main()
less than

print("I am in main()" if __name__ == "__main__" else "not in main")
I am in main()

a, b = 2, 3
c = a + b if a > 0 and b > 0 else 0
print(c)
5

how objects are created

class Egg:
    def __init__(self, style='fried'):  #initializing 
        self.style = style
    
    def whatKind(self):
        return self.style

def main():
    fried = Egg()
    scrambled = Egg('scrambled')
    print(fried.whatKind())
    print(scrambled.whatKind())

if __name__ == '__main__': main()
fried
scrambled

5. Varibales, Objects & Values

Top

  • Everthing in Python is an object
  • Every object has an ID, Type and Value
    • ID uniquely identifies a particular instance of an object
    • Cannot change for the life of the object
    • Type identifies the Class of an object which cannot change for the life of the object
#define varibale x
x = 49
#value of x
x
49

#id(x) a unique and constant for this object during its lifetime
id(x)
4549812688

type(x)
int

All varibales in Python are FIRST CLASS objects

x = 43 ## we are not changing the value, rather changing the reference hence the new id()
id(x)
4549812496

x = 49 ## if we switch back to the previous value we get the same id()/address
id(x)
4549812688

Most fundamental (primitive) types in Python are immutable :

  • numbers, string tupels

Mutable objects include:

  • lists, dictionaries, other objects depending upon implementation

Using Numbers

Top

def main():
    num = 42
    print('1.',type(num), num)
    num = 42.0
    print('2.',type(num), num)
    num = 42 / 9  # Floating point division
    print('3. floating point division', type(num), num)
    num = 42 // 9 # floor or integer division
    print('4. integer division', type(num), num)
    num = round(42 / 9)
    print('5. rounding',type(num), num)
    num = round(42 / 9, 2)
    print('6. rounding', type(num), num)
    num = 42 % 9
    print('7. Modulo/remainder', type(num), num)
    num = int(42.9)
    print('8. int() func', type(num), num)
    num = float(42)
    print('9. float() func', type(num), num)

if __name__ == "__main__": main()
1. <class 'int'> 42
2. <class 'float'> 42.0
3. floating point division <class 'float'> 4.666666666666667
4. integer division <class 'int'> 4
5. rounding <class 'int'> 5
6. rounding <class 'float'> 4.67
7. Modulo/remainder <class 'int'> 6
8. int() func <class 'int'> 42
9. float() func <class 'float'> 42.0

Using Strings

Top

#using \n for new line
s = 'this is a\nstring!'
rawString = r'this is a\nstring!' # this is called a raw string
print(s)
print(rawString)
this is a
string!
this is a\nstring!

Formatting

n = 42
s = 'this is a {} string'.format(n) #using format method of the string object
print(s)
this is a 42 string

# old way of doing this but will go away
n = 42
s = "this is a %s string" %n
print(s)
this is a 42 string

Creating a string that spans multiple lines

  • Using ''' ''' or """ """
s = '''
this is a string
line after line
of text and more
text.
'''

print(s)
this is a string
line after line
of text and more
text.

##escaping
s = '''\
this is a string \
line after line \
of text and more \
text.
'''
print(s)
this is a string line after line of text and more text.

Aggregating values with lists and tuples

x = (1, 2, 3)
print(type(x), x)
try:
    x.append(5)
except:
    print('Sorry, can\'t append Tuples are immutable')

y = [1, 2, 3]
y.append(5)
y.insert(2,4)
print(type(y), y)

a = 'this is a string'
print(type(a), a[10:])
<class 'tuple'> (1, 2, 3)
Sorry, can't append Tuples are immutable
<class 'list'> [1, 2, 4, 3, 5]
<class 'str'> string

Creating associative list with dictionaries

d = {'one':1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}
print(d, end='\n\n')

for k in d:
    print(k,d[k])

# to get it sorted
print('\n')
print('printing the dictionary sorted\n')
for k in sorted(d.keys()):
    print(k,d[k])
{'three': 3, 'one': 1, 'five': 5, 'four': 4, 'two': 2}

three 3
one 1
five 5
four 4
two 2


printing the dictionary sorted

five 5
four 4
one 1
three 3
two 2

Using the dict() constructor to create a dictionary

d = dict(
    one = 1,
    two = 2,
    three = 3,
    four = 4,
    five = 5
)
print(d)
{'three': 3, 'one': 1, 'five': 5, 'four': 4, 'two': 2}

d['seven'] = 7
d
{'five': 5, 'four': 4, 'one': 1, 'seven': 7, 'three': 3, 'two': 2}

Finding the type of identity of a varibale

Top

Remember: Varibales are references to objects

x = 42
print(id(x))
4297149840

y = 42
print(id(y))
4297149840

x == y # test for equality - compares VALUES
True

x is y # test if they are the same object - compares IDs
True

x = dict(x = 42)
x
{'x': 42}

id(x)
4369898888

y = dict( x= 42)
id(y)
4369612424

x == y
True

x is y # it's because a dictionary is immutable object
False

a = [1, 2, 3]
b = [1, 2, 3]
print(a is b) # not the same object
print(a == b) # same value
False
True

Specifying logical values with True and False

Top

a, b = 0, 1
a == b
False

a < b
True

a is b
False

a = True
print(type(a))
print(id(a))
<class 'bool'>
4296767152

b = True
print(id(b))
print(id(True))
print(id(False))
4296767152
4296767152
4296767120

Conditionals

IF-ELIF-ELSE

Top

v = 'seven'

if v == 'one':
    print('it is ONE')
elif v == 'two':
    print('it is TWO')
elif v == 'three':
    print('it is THREE')
else:
    print('it is something else')
it is something else

Other strategies for multiple choices

Alternatives to Switch or Case options we can use Dictionaries

Top

choices = dict(
one = 'first',
two = 'second',
three = 'third',
four = 'fourth',
five = 'fifth'
)

v = 'three'
print(choices[v])
third

issues with this approach if we use something outside the list it will generate an error Which we can catch with Try and Except

v = 'seven'
try:
    choices[v]
except:
    print('Did not find')
Did not find

another strategy using Dictionary .get() method

print(choices.get(v, 'Other')) #get method looks for value, if not found will print 'Other'
Other

Another option is using dictionaries in this approach:

{ 'option1' : function1,
  'option2' : function2,
  'option3' : function3,
  'option4' : function4 }[value]()
j = 'b'

result = {
    'a': lambda x: x * 5,
    'b': lambda x: x + 7,
    'c': lambda x: x - 2 
} [j](1)

# passing value 1 to function b which gives us 1 + 7 = 8
print(result)
8

One more example
we use the .get() which helps us define a default value

def test(x):
    return {
        'a': 1,
        'b': 2,
        'c': 3
    }.get(x, 'nothing')
i = 'b'
test(i)
2

test('c')
3

test(9)
'nothing'

choices = dict(
one = lambda x: x - 1,
two = lambda x: x- 2,
three = lambda x: x- 3,
four = lambda x: x- 4,
five = lambda x: x- 5
)

v = 'four'
print(choices.get(v, 'Nothing')(6))
2

Example of using Dictionary to make decisions

Top

def display(x):
    return x**2

def root(x):
    return x**0.5

even = {
1: lambda x: display(x),
2: lambda x: display(x),
3: lambda x: display(x),
4: lambda x: root(x),
9: lambda x: root(x)
}

num = int(input())

try:
    print(even.get(num, 'Doesn\'t Exist')(num))
except:
    print(num * 1.5)
3
9

Conditional Expression

a , b = 0, 1
v = "a greater than b" if a > b else "a is less than b"
print(v)
a is less than b

7. Loops

Top

While Loop

def main():
    # simple fibonacci series
    # the sum of two elements defines the next set
    a, b = 0, 1
    while b < 150:
        print(b, end=' ')
        a, b = b, a + b

if __name__ == "__main__": main()
1 1 2 3 5 8 13 21 34 55 89 144

Iterating with for

Note: readlines() and read().split('/n') are equivalent

Difference between read(), readlines() and readline()

readlines( )

The method readlines() reads until EOF using readline() and returns a list containing the lines

# Readlines() a list of strings for each line. 
fh = open('lines.txt')
content = fh.readlines()
fh.close()

print(content) #print all
print('\n')
print(content[0]) #show me first item of the list
print(content[-1]) #show me last item of the list
['This is the first line of text\n', 'This is the second line of text\n', 'This is the third line of text\n', 'This is the fourth line of text\n', 'This is the fifth line of text\n', 'This is the last line of text']


This is the first line of text

This is the last line of text

#looping example
for i in content:
    print(i)
This is the first line of text

This is the second line of text

This is the third line of text

This is the fourth line of text

This is the fifth line of text

This is the last line of text

readline( )

# Readline() - reads the first line only. So, looping will go through the characters from the first line
fh = open('lines.txt')
content = fh.readline()
fh.close()

print(content) #prints all content captured which is the first line
print(content[0]) #prints the firt character
print(content[-1]) #prints the last character in this case it is space so will look blank
This is the first line of text

T

#looping example
for i in content:
    print(i)
T
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f
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read( )

# Read() - reads the entire text 
# So, looping will go through the characters of the entire text
fh = open('lines.txt')
content =  fh.read()
fh.close()

print(content) #prints all content captured which is the first line
print('\n')
print(content[0]) #prints the firt character
print(content[-1]) #prints the last character in this case it is space so will look blank
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text


T
t

#looping example
for i in content:
    print(i)
T
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Iterating over readlines() example

  • using readlines() and print(end="") to avoid double \n since by default print(end ="\n")
def main():
    fh = open('lines.txt')
    for line in fh.readlines():
        print(line, end="")
    fh.close()
if __name__ == "__main__": main()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

# or can be done using .strip()

def main():
    fh = open('lines.txt')
    for line in fh.readlines():
        print(line.strip())
    fh.close()
if __name__ == "__main__": main()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

read() with print(end="") sice it reads characater by character. This way it keeps reading until line ends via '\n'

fh = open('lines.txt')
for line in fh.read():
    print(line, end="")
fh.close()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

Same as above, but accomplishing similar results with read() and .split('/n)

fh = open('lines.txt')
for line in fh.read().split('/n'):
    print(line)
fh.close()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

using readline() and split("/n")

def main():
    fh = open('lines.txt')
    for line in fh.readline().split('/n'):
        print(line)
    fh.close()
if __name__ == "__main__": main()
This is the first line of text

using readline() with print(end="")

def main():
    fh = open('./07 Loops/lines.txt')
    for line in fh.readline():
        print(line, end="")
    fh.close()
if __name__ == "__main__": main()
01 This is a line of text

Enumerating Iterators

def main():
    fh = open('lines.txt')
    for index, line in enumerate(fh.readlines()):
        print(index, line, end="")
    fh.close()
if __name__ == "__main__": main()
0 This is the first line of text
1 This is the second line of text
2 This is the third line of text
3 This is the fourth line of text
4 This is the fifth line of text
5 This is the last line of text

s = 'this is a string'

for i, c in enumerate(s):
    if c == 's': print('index {} is on s'.format(i))
index 3 is on s
index 6 is on s
index 10 is on s

Controlling loop flow with Break, Continue, and Else

Continue - to shortcut a for loop

# to skip over letter 's'
s = 'this is a string'
for c in s:
    if c == 's': continue
    print(c, end='')
thi i a tring

Break

# If I want to stop right at the first enconter of letter 's'
s = 'this is a string'
for c in s:
    if c == 's': break
    print(c, end='')
thi

Else

# else used when iterators get out of stuff to iterate
s = 'this is a string'
for c in s:
    print(c, end='')
else:
    print(' else')
this is a string else

# else can be used when a condition becomes false
s = 'this is a string'
i = 0
while (i < len(s)):
    print(s[i], end='')
    i += 1
else:
    print(' else done')
this is a string else done

8. Operators

Top

5 // 2
2

5 % 2
1

5 / 2
2.5

divmod(5, 3) # gives the result and remainder as a tuple
(1, 2)

num = 2
num += 1
print(num)
3

num -= 1
print(num)
2

num *=5
print(num)
10

num //=5
print(num)
2

num *=5
num /= 5
print(num)
2.0

Bitwise values

5
5

0b0101
5

# print out Binary Value
def b(n):
    print('{:08b}'.format(n))
b(5)
00000101

x , y = 0x55, 0xaa
b(x)
b(y)
b(x | y)
b(x & y)
b(x ^ y)
b(x ^ 0)
b(x ^ 0xff)
b( x << 4)
b( x >> 4)
b(~x)
01010101
10101010
11111111
00000000
11111111
01010101
10101010
10101010000
00000101
-1010110

Comparing identities with IS and IS NOT

There are times when we need to compare Objects by comparing their IDs and not just their values

x, y = 5, 6
x is y
False

x is not y
True

y = 5
x is y
True

x, y = [5], [5]
x is y #not the same IDs
False

print(id(y))
print(id(x))
4370870408
4370898504

x == y #same values
True

a = [1, 2, 3]
b = a #this points to the same object
a is b
True

#making a new copy
b = a[:]
a is b
False

Operating on parts of container with the slice operator

list = []
list = [0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
s = list[0:5]
s
[0, 1, 2, 3, 4]

for i in range(0,10): print(i, end=', ')
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 

list[:] = range(100)
print(list)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

list[27] #slice of one element
27

list[27:42] #slice with start and end
[27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41]

list[27:42:3] #slice with start and end for every third element
[27, 30, 33, 36, 39]

for i in list[27:43:3]: print(i)
27
30
33
36
39
42

list[27:43:3] = [99,99,99,99,99,99]
print(list)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 99, 28, 29, 99, 31, 32, 99, 34, 35, 99, 37, 38, 99, 40, 41, 99, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

9. Regular Expressions

Top

Searching with Regular Expressions

import re

def main():
    fh = open('raven.txt')
    for i, line in enumerate(fh.readlines()):
        if re.search('(Len|Neverm)ore', line): #matches Lenore or Nevermore
            print(i, line, end='')

if __name__ == "__main__": main()
    
10 From my books surcease of sorrow--sorrow for the lost Lenore--
11 For the rare and radiant maiden whom the angels name Lenore--
31 And the only word there spoken was the whispered word, “Lenore!”
32 This I whispered, and an echo murmured back the word, “Lenore!”--
54 Quoth the raven “Nevermore.”
61 With such name as “Nevermore.”
68 Then the bird said “Nevermore.”
82 Meant in croaking “Nevermore.”
95 Respite--respite and nepenthe from thy memories of Lenore;
96 Quaff, oh quaff this kind nepenthe and forget this lost Lenore!”
97 Quoth the raven, “Nevermore.”
104 Quoth the raven, “Nevermore.”
109 It shall clasp a sainted maiden whom the angels name Lenore--
110 Clasp a rare and radiant maiden whom the angels name Lenore.”
111 Quoth the raven, “Nevermore.”
118 Quoth the raven, “Nevermore.”

import re

def main():
    fh = open('raven.txt')
    for i, line in enumerate(fh.readlines()):
        match = re.search('(Len|Neverm)ore', line)
        if match: #matches Lenore or Nevermore
            print(i, match.group())

if __name__ == "__main__": main()
    
10 Lenore
11 Lenore
31 Lenore
32 Lenore
54 Nevermore
61 Nevermore
68 Nevermore
82 Nevermore
95 Lenore
96 Lenore
97 Nevermore
104 Nevermore
109 Lenore
110 Lenore
111 Nevermore
118 Nevermore

Replacing with Regular Expressions

import re

def main():
    fh = open('raven.txt')
    for i, line in enumerate(fh.readlines()):
         match = re.search('(Len|Neverm)ore', line) #matches Lenore or Nevermore
         if match:
            print(i, line.replace(match.group(), '###'), end='')
if __name__ == "__main__": main()
10 From my books surcease of sorrow--sorrow for the lost ###--
11 For the rare and radiant maiden whom the angels name ###--
31 And the only word there spoken was the whispered word, “###!”
32 This I whispered, and an echo murmured back the word, “###!”--
54 Quoth the raven “###.”
61 With such name as “###.”
68 Then the bird said “###.”
82 Meant in croaking “###.”
95 Respite--respite and nepenthe from thy memories of ###;
96 Quaff, oh quaff this kind nepenthe and forget this lost ###!”
97 Quoth the raven, “###.”
104 Quoth the raven, “###.”
109 It shall clasp a sainted maiden whom the angels name ###--
110 Clasp a rare and radiant maiden whom the angels name ###.”
111 Quoth the raven, “###.”
118 Quoth the raven, “###.”

Resusing Regular Expressions with re.compile

import re

def main():
    fh = open('raven.txt')
    pattern = re.compile('(Len|Neverm)ore', re.IGNORECASE) # more efficient since we compile the pattern only once
    for i, line in enumerate(fh.readlines()):
        if re.search(pattern, line): #matches Lenore or Nevermore
            print(i, line, end='')

if __name__ == "__main__": main()
10 From my books surcease of sorrow--sorrow for the lost Lenore--
11 For the rare and radiant maiden whom the angels name Lenore--
31 And the only word there spoken was the whispered word, “Lenore!”
32 This I whispered, and an echo murmured back the word, “Lenore!”--
54 Quoth the raven “Nevermore.”
61 With such name as “Nevermore.”
68 Then the bird said “Nevermore.”
75 Of “Never--nevermore.”
82 Meant in croaking “Nevermore.”
89 _She_ shall press, ah, nevermore!
95 Respite--respite and nepenthe from thy memories of Lenore;
96 Quaff, oh quaff this kind nepenthe and forget this lost Lenore!”
97 Quoth the raven, “Nevermore.”
104 Quoth the raven, “Nevermore.”
109 It shall clasp a sainted maiden whom the angels name Lenore--
110 Clasp a rare and radiant maiden whom the angels name Lenore.”
111 Quoth the raven, “Nevermore.”
118 Quoth the raven, “Nevermore.”
125 Shall be lifted--nevermore!

import re

def main():
    fh = open('raven.txt')
    pattern = re.compile('(Len|Neverm)ore', re.IGNORECASE) # more efficient since we compile the pattern only once
    for i, line in enumerate(fh.readlines()):
        if re.search(pattern, line): #matches Lenore or Nevermore
            print(i, pattern.sub('###',line), end='')

if __name__ == "__main__": main()
10 From my books surcease of sorrow--sorrow for the lost ###--
11 For the rare and radiant maiden whom the angels name ###--
31 And the only word there spoken was the whispered word, “###!”
32 This I whispered, and an echo murmured back the word, “###!”--
54 Quoth the raven “###.”
61 With such name as “###.”
68 Then the bird said “###.”
75 Of “Never--###.”
82 Meant in croaking “###.”
89 _She_ shall press, ah, ###!
95 Respite--respite and nepenthe from thy memories of ###;
96 Quaff, oh quaff this kind nepenthe and forget this lost ###!”
97 Quoth the raven, “###.”
104 Quoth the raven, “###.”
109 It shall clasp a sainted maiden whom the angels name ###--
110 Clasp a rare and radiant maiden whom the angels name ###.”
111 Quoth the raven, “###.”
118 Quoth the raven, “###.”
125 Shall be lifted--###!

10. Exceptions

Top

Handling Excpetions

def main():
    try:
        fh = open('lins.txt')
    except IOError as e:
        print('could not open the file. come back tomorrow: ', e)
    else:
        for line in fh: print(line.strip()) # removes trailing lines

if __name__ == "__main__": main()
could not open the file. come back tomorrow:  [Errno 2] No such file or directory: 'lins.txt'

Raising Exceptions

def main():
    try:
        for line in readfile('lies.doc'): 
            print(line.strip()) # removes trailing lines
    except IOError as e:
        print('cannot read file: ', e)
    except ValueError as e:
        print('bad filename: ', e)
        

def readfile(filename):
    if filename.endswith('.txt'):
        fh = open(filename)
        return fh.readlines()
    else: 
        raise ValueError('Filename must end with .txt')

if __name__ == "__main__": main()
bad filename:  Filename must end with .txt

11. Functions

Top

Defining functions with arguments: Default values & None

def main():
    testfunc()

def testfunc():
    print('This is a test function')

if __name__ == "__main__": main()
This is a test function

def main():
    testfunc()

def testfunc():
    pass #to avoid an error, can be used as a placeholder

if __name__ == "__main__": main()

Using Paremeters & default values

  • Parameters can be required or optionals
  • Function arguments must be initialized
  • To avoid errors, we can use defaut values
def main():
    testfunc(42, 1)

def testfunc(number = 1, another = 42, onemore= 75):
    print('This is a test function',number, another, onemore )

if __name__ == "__main__": main()
This is a test function 42 1 75

Making the parameter options using None

None is a special value that we can also test for

def main():
    testfunc(42, 1)
def testfunc(number = 1, another = None, onemore= 75):
    if another is None:
        another = 112
    print('This is a test function',number, another, onemore )

if __name__ == "__main__": main()
This is a test function 42 1 75

Using lists of arguments

We get a Tuple

def main():
    testfunc(1, 2, 3, 4)

def testfunc(*args):
    print('This is a tuple')
    for n in args: print(n, end= ' ')

if __name__ == "__main__": main()
This is a tuple
1 2 3 4 

def main():
    testfunc(1, 2, 3, 4)

def testfunc(number, another, *args):
    print('Your arguemnts: ', number, another, args)

if __name__ == "__main__": main()
Your arguemnts:  1 2 (3, 4)

Using named function arguments

using (**kwargs) = stands for Keyboard Arguments

def main():
    testfunc(one = 1, two = 2, four = 42)

def testfunc(**kwargs):
    print('This is a test function', kwargs['one'], kwargs['two'], kwargs['four'])

if __name__ == "__main__": main()
This is a test function 1 2 42

Combination of different argument types:

def main():
    testfunc(5, 6, 7, 8, 9, 10, one = 1, two = 2, four = 42)

def testfunc(this, that ,other, *args, **kwargs):
    print('This is a test function', 
          this, that, other, args,
          kwargs['one'], kwargs['two'], kwargs['four'])

if __name__ == "__main__": main()
This is a test function 5 6 7 (8, 9, 10) 1 2 42

def main():
    testfunc(5, 6, 7, 8, 9, 10, one = 1, two = 2, four = 42)

def testfunc(this, that ,other, *args, **kwargs):
    for k in kwargs: print(k, kwargs[k]) #wont maintain order
    for n in args: print(n) #tuples do maintain order

if __name__ == "__main__": main()
four 42
one 1
two 2
8
9
10

Returning values from functions

def main():
    for n in testfunc(): print(n, end= ' ')

def testfunc():
    return range(25)

if __name__ == '__main__': main()
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Generator Function

def main():
    print("This is the functions.py file.")
    for i in inclusive_range(2,25,3):
        print(i, end = ' ')

def inclusive_range(*args):
    numargs = len(args)
    if numargs < 1: raise TypeError('requires at least one argument')
    elif numargs == 1: 
        stop = args[0]
        start = 0
        step = 1
    elif numargs == 2:
        (start, stop) = args
        step = 1
    elif numargs == 3:
        (start, stop, step) = args
    else: 
        raise TypeError('inclusive_range expected at most 3 arguments, got {}'.format(numargs))
    
    i = start
    try:
        while i <= stop:
            yield i # next time it run it will resume
            i += step
    except TypeError as e:
        print(e)
    
if __name__ == "__main__": main()
This is the functions.py file.
2 5 8 11 14 17 20 23

12. Classes

Top

  • Classes are how we create our own objects
  • A class is the blueprint for an object
  • An object is an instance of a class
class Duck:
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')

def main():
    donald = Duck() #donals is an objet which is an instance of class Duck
    donald.quack()
    donald.walk()

if __name__ == "__main__": main()
Quaaack!
Walks like a duck.

Using Methods

  • methods are functions
  • first argument is always (self) which is a refernce to the object
  • constructor method _init_
    • constructors are great for initializing values
class Duck:
    def __init__(self, value):
        print('I am a Constructor')
        self._v = value #creating a local variable that is an attribute of the object i.e. donald
        
    def quack(self, value):
        print('Quaaack!', self._v, value) #now we can use the local varibale

    def walk(self):
        print('Walks like a duck.', self._v)

def main():
    donald = Duck(47) 
    donald.quack(12) #donald is being passed as self
    donald.walk()
    frank = Duck(100)
    frank.quack(10)
    frank.walk()
    

if __name__ == "__main__": main()
I am a Constructor
Quaaack! 47 12
Walks like a duck. 47
I am a Constructor
Quaaack! 100 10
Walks like a duck. 100

Using Object Data

  • It is recommended to access local varibales in a class using accessor methods
    • Set and Get methods as an example
class Duck:
    def __init__(self, color = 'white'):
        self._color = color # using _ is to help us remember that this is a local variable
        
        
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')
        
    def set_color(self, color): 
        self._color = color
     
    def get_color(self):
        return self._color

def main():
    donald = Duck() #donals is an objet which is an instance of class Duck
    print(donald.get_color())
    donald.set_color('blue')
    print(donald.get_color())

if __name__ == "__main__": main()
white
blue

If there are many setters that we need to use and call it can get overwhilming. Another option is to use Dictionary (keyword arguments)

class Duck:
    def __init__(self, **kwargs):
        self._color = kwargs.get('color','white') #having a default value         
        self._feet = kwargs.get('feet')
        
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')
        
    def set_color(self, color): 
        self._color = color
     
    def get_color(self):
        return self._color
    
    def get_feet(self):
        return self._feet

def main():
    donald = Duck(color='blue')
    james = Duck()
    print(donald.get_color())
    print(james.get_color())
    smith = Duck(feet=2)
    print(smith.get_feet())
    

if __name__ == "__main__": main()
blue
white
2

Dictionary .get() built in function and defaults

j = {'color': 'blue', 'feet': 4}
print(j.get('color', 'black'))

s = {'feet': 4}
print(s.get('color', 'black'))
blue
black

instead of having differernt local varibales we can use a dictionary

class Duck:
    def __init__(self, **kwargs):
        self.varibales = kwargs
        
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')
        
    def set_color(self, color): 
        self.varibales['color'] = color
    
    def set_feet(self, feet):
        self.varibales['feet'] = feet
     
    def get_color(self):
        return self.varibales.get('color', None)
    
    def get_feet(self):
        return self.varibales.get('feet', 4)

def main():
    donald = Duck(color='blue')
    james = Duck()
    print(donald.get_color())
    print(james.get_color())
    smith = Duck()
    print(smith.get_feet())
    

if __name__ == "__main__": main()
blue
None
4

Make the setters scale as well we can make another modification

Storing Object data in a Dictionay - the code below is scalable and flexible

class Duck:
    def __init__(self, **kwargs):
        self.varibales = kwargs
        
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')
        
    def set_variables(self, k, v):
        self.varibales[k] = v
    
    def get_varibales(self, k):
        return self.varibales.get(k, None)

def main():
    donald = Duck(feet = 2)
    donald.set_variables('color','pink')
    print(donald.get_varibales('feet'))
    print(donald.get_varibales('color'))

    
if __name__ == "__main__": main()
2
pink

Understanding Inheritance

class Animal:
    def talk(self): print('I have something to say')
    def walk(self): print('Hey, I''m walking'' here!')
    def clothes(self): print('I have nice clothes')    

class Duck(Animal): #now Duck inherits all properties of animal
    def quack(self):
        print('Quaaack!')

    def walk(self):
        #if we want to access the paretn method we use super()
        super().walk()
        print('Walks like a duck.')

def main():
    donald = Duck()
    donald.quack()
    donald.walk() #the Duck walk overwrties the parent, to access both we used super()
    donald.clothes() #from parent
    donald.talk() # from parent

if __name__ == "__main__": main()
Quaaack!
Hey, Im walking here!
Walks like a duck.
I have nice clothes
I have something to say

class Dog(Animal):
    def clothes(self): print('I have brown and white fur')

fido = Dog()
fido.clothes()
fido.talk()
I have brown and white fur
I have something to say

Applying polymorphism to classes

class Duck:
    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')
    
    def bark(self):
        print('Duck cannot bark')
    
    def fur(self):
        print('The duck has feathers')


donald = Duck()
donald.quack()
donald.walk()
Quaaack!
Walks like a duck.

class Dog:
    def bark(self):
        print('Woof!')
        
    def fur(self): 
        print('the dog has brown and white fur')
    
    def walk(self):
        print('Walks like a dog')
    
    def quack(self):
        print('The dog cannot quack')
        
fido = Dog()
fido.bark()
fido.fur()
Woof!
the dog has brown and white fur

By making both classes have common methods we now can

for o in (donald, fido):
    o.quack()
    o.walk()
    o.bark()
    o.fur()
Quaaack!
Walks like a duck.
Duck cannot bark
The duck has feathers
The dog cannot quack
Walks like a dog
Woof!
the dog has brown and white fur
Duck cannot bark
The duck has feathers
The dog cannot quack
Walks like a dog

Polymorphism

def in_the_forest(dog):
    dog.bark()
    dog.fur()

def in_the_pond(duck):
    duck.quack()
    duck.walk()
    
in_the_forest(donald)
in_the_pond(fido)
Duck cannot bark
The duck has feathers
The dog cannot quack
Walks like a dog

Using generators __iter__

An object that can be used in the context of itterable

def main():
    o = range(25)
    for i in o: print(i, end = ' ')

if __name__ == "__main__": main()
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 

class inclusive_range:
    def __init__(self, *args):
        numargs = len(args)
        if numargs < 1: raise TypeError('requires at least one argument')
        elif numargs == 1:
            self.stop = args[0]
            self.start = 0
            self.step = 1
        elif numargs == 2:
            (self.start, self.stop) = args
            self.step =1 
        elif numargs == 3:
            (self.start, self.stop, self.step) = args
        else: raise TypeError('expected at most 3 arguments, got {}'.format(numargs))

    
    def __iter__(self): #makes the object an iterable object
        i = self.start
        while i <= self.stop:
            yield i
            i += self.step
    
for i in inclusive_range(5, 25, 5): print(i, end = ' ')
5 10 15 20 25

Using decorators : Special functions that return other functions

class Duck:
    def __init__(self, **kwargs):
        self.properties = kwargs

    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')

    def get_properties(self):
        return self.properties
    
    def set_property(self, key, value):
        print(key, value)
        self.properties[key] = value

    def get_property(self, key):
        return self.properties.get(key, None)

donald = Duck(color = 'blue')
print(donald.get_property('color'))


blue

donald.set_property('feet', 2)
print(donald.get_property('feet'))
feet 2
2

Using @property to start declaring .setter and .deleter

class Duck:
    def __init__(self, **kwargs):
        self.properties = kwargs

    def quack(self):
        print('Quaaack!')

    def walk(self):
        print('Walks like a duck.')

    def get_properties(self):
        return self.properties
    
    def set_property(self, key, value):
        print(key, value)
        self.properties[key] = value

    def get_property(self, key):
        return self.properties.get(key, None)

    @property #turns this function as an accessor
    def color(self):
        return self.properties.get('color', None)
    
    @color.setter #declare a setter
    def color(self, c):
        self.properties['color'] = c
    
    @color.deleter
    def color(self):
        del self.properties['color']

donald = Duck()
donald.color = 'blue'
print(donald.color)
blue

13. String Methods

Top

Strings are objets

We can operate on a string like objects without using varibale assignment

'This is a string'.upper()
'THIS IS A STRING'

'this is a string'.title()
'This Is A String'

'this is a string {}'.format(42)
'this is a string 42'

Common string methods

Example:

upper(), lower(), strip(), rstrip(), replace(), isalnum(), title(), isalpha(), isprintable(), isdigit(), capitalize(), format(), swapcase(), find()

s = 'this is a string'
s.capitalize()
'This is a string'

s.upper()
'THIS IS A STRING'

'This Is A String'.swapcase()
'tHIS iS a sTRING'

s.find('is') #finds the position 
2

s.replace('this', 'that')
'that is a string'

String is immutable , so there methods return a new string while original is unchanged

s #still the same
'this is a string'

id(s)
4368522024

newstring = s.upper()
id(newstring) # new id
4368522888

i = s
id(i) #same id
4368522024

'  this is a string   '.strip() #remove whitespace by default
'this is a string'

'    this is a string  '.rstrip() #remove white space in end
'    this is a string'

s1 = 'this is a string\n'
s1
'this is a string\n'

s1.strip() #remove the new line \n
'this is a string'

s1.rstrip('\n') #same effect
'this is a string'

s.isalnum() #returns False since the string contains spaces
False

'thisisastring'.isalnum()
True

'thisisstring'.isalpha()
True

'1234'.isdigit()
True

s.isdigit()
False

s.isprintable()
True

Formatting strings with str.format

Remember: Strings are immutable in Python so changes mean a new string is created

a, b = 5, 42
print(a, b)
5 42

'this is {}, that is {}'.format(a, b)
'this is 5, that is 42'

s = 'this is {}, that is {}'
id(s)
4368620256

new = s.format(a, b)
id(new)
4369101280

j = s
id(j)
4368620256

Changing positional order

'this is {}, that is {}'.format(b, a) #change the varibale orders
'this is 42, that is 5'

'this is {0}, that is {1}'.format(a, b)
'this is 5, that is 42'

'this is {1}, that is {0}'.format(a, b)
'this is 42, that is 5'

'this is {1}, that is {1}'.format(a, b)
'this is 42, that is 42'

'this is {bob}, that is {fred}'.format(bob = a, fred = b)
'this is 5, that is 42'

d = dict(bob = a, fred = b)
'this is {bob}, that is {fred}'.format(**d)
'this is 5, that is 42'

Splitting and Joining Strings

s = 'This is a string of words'
s.split() #splits by whitespace by default
['This', 'is', 'a', 'string', 'of', 'words']

s.split('i') #split on i
['Th', 's ', 's a str', 'ng of words']

words = s.split()
for w in words: print(w)
This
is
a
string
of
words

new = ':'.join(words)
new
'This:is:a:string:of:words'

','.join(words)
'This,is,a,string,of,words'

' '.join(words)
'This is a string of words'

Finding and using string methods

Python documentation

s = 'this is a string'
new = s.center(80) #80 characters
new
'                                this is a string                                '

len(new)
80

14. Containers

Top

Tuples can be created using the comma operator like this

t = 1,2,3,4,5
t
(1, 2, 3, 4, 5)

How to create a tuple with ONE element?

t = (1) # this is not correct, it will produce an Int
print(t)
print(type(t))
1
<class 'int'>

t = 1,
print(t)
print(type(t))
(1,)
<class 'tuple'>

t = tuple(range(25))
print(t)
print(type(t))
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
<class 'tuple'>

x = []
type(x)
list

x = list(range(25))
print(x)
print(type(x))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
<class 'list'>

Operating on sequences with built-in methods

t = tuple(range(25))
print(t)
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)

10 in t
True

50 in t
False

50 not in t
True

x = list(range(20))
print(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

10 in x
True

20 in x
False

t.count(4)
1

t.index(6)
6

x.append(100)
x.extend(range(20))
print(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

x.insert(0, 25)
print(x)
[25, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

x.remove(12)
print(x)
[25, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

del x[12]
print(x)
[25, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

x.pop()
19

print(x)
[25, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]

x.pop(0)
25

print(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, 18, 19, 100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]

Organizing data with dictionaries

d = {'one': 1, 'two': 2, 'three': 3}
d
{'one': 1, 'three': 3, 'two': 2}

d = dict(one = 1, two = 2, three = 3)
d
{'one': 1, 'three': 3, 'two': 2}

x = dict(four = 4, five = 5, six = 6)
s = dict(**x, **d)
print(s)
{'one': 1, 'five': 5, 'four': 4, 'three': 3, 'two': 2, 'six': 6}

'four' in s
True

'four' in d
False

for k,v in s.items(): print(k,v)
one 1
five 5
four 4
three 3
two 2
six 6

Getting exception and using .get to avoid

x['three']
---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

<ipython-input-112-05f923b6ba3c> in <module>()
----> 1 x['three']


KeyError: 'three'

x.get('three')
x.get('three', 'not found')
'not found'

del x['four']
print(x)
{'five': 5, 'six': 6}

x.pop('five')
5

x
{'six': 6}

def printMe():
    print('hello world')

f = dict(one = printMe, two = printMe)
for k in f.values() : print(k)
<function printMe at 0x104848f28>
<function printMe at 0x104848f28>

for k in f.values() : print(k())
hello world
None
hello world
None

Operating on character data with bytes and byte arrays

def main():
    fin = open('./14 Containers/utf8.txt','r', encoding='utf_8')
    fout = open('utf8.html', 'w')
    outbytes = bytearray()
    for line in fin:
        for c in line:
            if ord(c) > 127:
                outbytes += bytes('&#{:04d};'.format(ord(c)), encoding = 'utf_8')
            else:
                outbytes.append(ord(c))
    outstr = str(outbytes, encoding = 'utf_8')
    print(outstr, file = fout)
    print(outstr)
    print('Done.')

if __name__ == "__main__": main()
This is a UTF-8 file. 
It has some interesting characters in it. 
&#1641;(&#0865;&#3663;&#0815;&#0865;&#3663;)&#1782;

Done.

15. File I/O

Top

Opening Files

def main():
    f = open('lines.txt') # read mode is the default r
    for line in f:
        print(line, end = '')

if __name__ == "__main__": main()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

def main():
    f = open('lines.txt', 'r') 
    for line in f.readlines():
        print(line, end = '')

if __name__ == "__main__": main()
This is the first line of text
This is the second line of text
This is the third line of text
This is the fourth line of text
This is the fifth line of text
This is the last line of text

Reading and Writing Text files

def main():
    infile = open('lines.txt') # read mode is the default r
    outfile = open('new.txt', 'w')
    for line in infile:
        print(line, file = outfile, end = '')
    print('Done.')

if __name__ == "__main__": main()
Done.

Working with big files
Reading in buffer bytes, for examples infile.read(50000) means read at most 50000 bytes from infile, then read the next 50000 bytes. This way we are reading in chunks instead of one line at a time.

file.read([size])

Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes). If the size argument is negative or omitted, read all data until EOF is reached. The bytes are returned as a string object. An empty string is returned when EOF is encountered immediately. (For certain files, like ttys, it makes sense to continue reading after an EOF is hit.) Note that this method may call the underlying C function fread() more than once in an effort to acquire as close to size bytes as possible. Also note that when in non-blocking mode, less data than was requested may be returned, even if no size parameter was given.

buffer is not the file but what you last read from the file. len(buffer) will evaluate to False when buffer is empty, i.e. when there's no more data to read from the file.

def main():
    buffersize = 50000
    infile = open('bigfile.txt', 'r') 
    outfile = open('newbigfile.txt', 'w')
    buffer = infile.read(buffersize) #
    
    while len(buffer):
        outfile.write(buffer)
        print('.', end = '')
        buffer = infile.read(buffersize)
    print()
    print('Done.')

if __name__ == "__main__": main()
............................................
Done.

Reading and writing binary files

There is a difference when working with Text files vs working with Binary files

def main():
    buffersize = 50000
    infile = open('olives.jpg', 'rb')  #open in read binary mode
    outfile = open('new.jpg', 'wb')
    buffer = infile.read(buffersize)
                        
    while len(buffer):
        outfile.write(buffer)
        print('.', end = '')
        buffer = infile.read(buffersize)
    print()
    print('Done.')
    
if __name__ == "__main__": main()
..
Done.

16. Databases

Top

Creating a database with SQLite 3

import sqlite3

def main():
    db = sqlite3.connect('test.db')
    db.execute('drop table if exists test')
    db.execute('create table test (t1 text, i1 int)')
    db.execute('insert into test (t1, i1) values (?,?)', ('one', 1))
    db.execute('insert into test (t1, i1) values (?,?)', ('two', 2))
    db.execute('insert into test (t1, i1) values (?,?)', ('three', 3))
    db.execute('insert into test (t1, i1) values (?,?)', ('four', 4))
    db.commit()
    cursor = db.execute('select i1, t1 from test order by i1')
    
    for row in cursor:
        print(row)  #data comes back in tuples
    
if __name__ == "__main__": main()
(1, 'one')
(2, 'two')
(3, 'three')
(4, 'four')

row is an interable in the example below because we used row_factory to create a row object. We can convert it into a Dictionary

import sqlite3

def main():
    db = sqlite3.connect('test.db')
    db.row_factory = sqlite3.Row #created row objects
    db.execute('drop table if exists test')
    db.execute('create table test (t1 text, i1 int)')
    db.execute('insert into test (t1, i1) values (?,?)', ('one', 1))
    db.execute('insert into test (t1, i1) values (?,?)', ('two', 2))
    db.execute('insert into test (t1, i1) values (?,?)', ('three', 3))
    db.execute('insert into test (t1, i1) values (?,?)', ('four', 4))
    db.commit()
    cursor = db.execute('select i1, t1 from test order by i1')
    
    for row in cursor:
        print(dict(row))  #data comes back in tuples
    
if __name__ == "__main__": main()

{'i1': 1, 't1': 'one'}
{'i1': 2, 't1': 'two'}
{'i1': 3, 't1': 'three'}
{'i1': 4, 't1': 'four'}

db = sqlite3.connect('test.db')
db.row_factory = sqlite3.Row
cursor = db.execute('select i1, t1 from test order by i1')
    
for row in cursor:
    print(row['t1'], row['i1'])  #data comes back in tuples
one 1
two 2
three 3
four 4

Creating, retrieving, updating and deleting records (CRUD)

import sqlite3

def insert(db, row):
    db.execute('insert into test (t1, i1) values (?, ?)', (row['t1'], row['i1']))
    db.commit()

def retrieve(db, t1):
    cursor = db.execute('select * from test where t1 = ?', (t1,))
    return cursor.fetchone()

def update(db, row):
    db.execute('update test set i1 = ? where t1 = ?', (row['i1'], row['t1']))
    db.commit()

def delete(db, t1):
    db.execute('delete from test where t1 = ?', (t1,))
    db.commit()

def disp_rows(db):
    cursor = db.execute('select * from test order by t1')
    for row in cursor:
        print('  {}: {}'.format(row['t1'], row['i1']))

def main():
    db = sqlite3.connect('test2.db')
    db.row_factory = sqlite3.Row
    print('Create table test')
    db.execute('drop table if exists test')
    db.execute('create table test ( t1 text, i1 int )')

    print('Create rows')
    insert(db, dict(t1 = 'one', i1 = 1))
    insert(db, dict(t1 = 'two', i1 = 2))
    insert(db, dict(t1 = 'three', i1 = 3))
    insert(db, dict(t1 = 'four', i1 = 4))
    disp_rows(db)

    print('Retrieve rows')
    print(dict(retrieve(db, 'one')), dict(retrieve(db, 'two')))

    print('Update rows')
    update(db, dict(t1 = 'one', i1 = 101))
    update(db, dict(t1 = 'three', i1 = 103))
    disp_rows(db)

    print('Delete rows')
    delete(db, 'one')
    delete(db, 'three')
    disp_rows(db)

if __name__ == "__main__": main()
Create table test
Create rows
  four: 4
  one: 1
  three: 3
  two: 2
Retrieve rows
{'i1': 1, 't1': 'one'} {'i1': 2, 't1': 'two'}
Update rows
  four: 4
  one: 101
  three: 103
  two: 2
Delete rows
  four: 4
  two: 2

Creating a Database Object

class database:
    def __init__(self, **kwargs):
        self.filename = kwargs.get('filename')
        self.table = kwargs.get('table', 'test')
    
    def sql_do(self, sql, *params):
        self._db.execute(sql, params)
        self._db.commit()
    
    def insert(self, row):
        self._db.execute('insert into {} (t1, i1) values (?, ?)'.format(self._table), (row['t1'], row['i1']))
        self._db.commit()
    
    def retrieve(self, key):
        cursor = self._db.execute('select * from {} where t1 = ?'.format(self._table), (key,))
        return dict(cursor.fetchone())
    
    def update(self, row):
        self._db.execute(
            'update {} set i1 = ? where t1 = ?'.format(self._table),
            (row['i1'], row['t1']))
        self._db.commit()
    
    def delete(self, key):
        self._db.execute('delete from {} where t1 = ?'.format(self._table), (key,))
        self._db.commit()

    def disp_rows(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            print('  {}: {}'.format(row['t1'], row['i1']))

    def __iter__(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            yield dict(row)

    @property
    def filename(self): return self._filename

    @filename.setter
    def filename(self, fn):
        self._filename = fn
        self._db = sqlite3.connect(fn)
        self._db.row_factory = sqlite3.Row

    @filename.deleter
    def filename(self): self.close()

    @property
    def table(self): return self._table
    @table.setter
    def table(self, t): self._table = t
    @table.deleter
    def table(self): self._table = 'test'

    def close(self):
            self._db.close()
            del self._filename

def main():
    db = database(filename = 'test.db', table = 'test')

    print('Create table test')
    db.sql_do('drop table if exists test')
    db.sql_do('create table test ( t1 text, i1 int )')

    print('Create rows')
    db.insert(dict(t1 = 'one', i1 = 1))
    db.insert(dict(t1 = 'two', i1 = 2))
    db.insert(dict(t1 = 'three', i1 = 3))
    db.insert(dict(t1 = 'four', i1 = 4))
    for row in db: print(row)

    print('Retrieve rows')
    print(db.retrieve('one'), db.retrieve('two'))

    print('Update rows')
    db.update(dict(t1 = 'one', i1 = 101))
    db.update(dict(t1 = 'three', i1 = 103))
    for row in db: print(row)

    print('Delete rows')
    db.delete('one')
    db.delete('three')
    for row in db: print(row)

if __name__ == "__main__": main()
Create table test
Create rows
{'i1': 4, 't1': 'four'}
{'i1': 1, 't1': 'one'}
{'i1': 3, 't1': 'three'}
{'i1': 2, 't1': 'two'}
Retrieve rows
{'i1': 1, 't1': 'one'} {'i1': 2, 't1': 'two'}
Update rows
{'i1': 4, 't1': 'four'}
{'i1': 101, 't1': 'one'}
{'i1': 103, 't1': 'three'}
{'i1': 2, 't1': 'two'}
Delete rows
{'i1': 4, 't1': 'four'}
{'i1': 2, 't1': 'two'}

17. Modules

Top

Using Standard Library Modules

Example: sys, os, urllib, random, datetime

import sys

def main():
    print('Python version {}.{}.{}'.format(*sys.version_info))
    print('Platform Name: ', sys.platform)
    
    import os #can import modules selectively inside a function for example
    print('OS Name: ', os.name)
    print(os.getenv('PATH'))
    print('Working Directory: ', os.getcwd())
    print('set of random bytes : ', os.urandom(25))
    


if __name__ == "__main__": main()
Python version 3.5.5
Platform Name:  darwin
OS Name:  posix
/anaconda3/bin:/Library/TeX/texbin:/Applications/Genymotion.app/Contents/MacOS/tools:/Users/tarekatwan/.nvm/versions/node/v9.2.0/bin:/anaconda3/bin:/Users/tarekatwan/bin:/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/TeX/texbin:/opt/X11/bin
Working Directory:  /Users/tarekatwan/Documents/GitHubRepos/Learn-Python-3
set of random bytes :  b'\x0e\x89m\x14sx\x84O\xf8\xb8r\x12\xc9\x05\x83\x08m\xa9`\xaf\x9e\xe6/\xe9c'

import urllib.request
url = "http://bw.org/"
page = urllib.request.urlopen(url)

for line in page: print(str(line, encoding = 'utf_8'), end = '')
<title> Bill Weinman </title>

<link rel="SHORTCUT ICON" href="https://i.bw.org/bw/bw.ico" />
<link rel="alternate" type="application/rss+xml" title="Bill Weinman's Technology Blog" href="http://billweinman.wordpress.com/feed/" />
<link rel="stylesheet" type="text/css" href="https://i.bw.org/css/main.css" />
<!--
    This is what old klugifed legacy code looks like. Horrible, ain't it? 
-->
</head>

<body bgcolor=white background="https://i.bw.org/bw/bw-bg.png" text="#000000" link="#333333" vlink="#333333" alink="#663333"
  leftmargin=8>

<a name="top"></a>
<table cellpadding=0 cellspacing=0 border=0><tr><td height=5></td><tr></table>

<table width=800 height="75%" cellspacing=0 cellpadding=0 border=0>
  <tr valign=top>
    <td width=100 valign=top align=center>

<a href="https://bw.org/"><img src="https://i.bw.org/bw/bw-logo-100.gif" width=100 height=50 alt="BW" border=0></a>

<table cellpadding=0 cellspacing=0 border=0><tr><td height=10></td><tr></table>

          <!-- menu -->
      <table cellpadding=0 cellspacing=0 border=0><tr><td bgcolor=white>
      <table cellpadding=0 cellspacing=1 border=0>
        <tr><td width=100 bgcolor=black>
        <table width="100%" cellpadding=0 cellspacing=2 border=0>
        <tr><td bgcolor=black width="100%" align=center>
          <span class="menu-title">Main Menu</span>
        </td></tr>
        <tr><td bgcolor=white width="100%" align=left class=small>
          <font face="verdana,helvetica,arial" size=1 color=black>
          <a class=menu href="http://bw.org/" title="BW Home">Home</a><br>
          <a class=menu href="http://bw.org/contact/">Contact Bill</a><br>
          <a class=menu href="http://bw.org/ldcfaq">lynda.com FAQ</a><br>
          <a class=menu href="http://bw.org/u/fb01" title="BW on Facebook">Facebook</a><br>
          <a class=menu href="http://bw.org/u/li01" title="BW on Linked In">Linked In</a><br>
          <a class=menu href="http://bw.org/u/tw01" title="BW on Twitter">Twitter</a><br>
          <a class=menu href="http://amtp.bw.org/" title="AMTP -- a replacement for SMTP">AMTP</a><br>
          <a class=menu href="http://bw.org/bio.html" title="About Bill">Bio</a><br>
          <a class=menu href="http://bw.org/available/">Hire Bill</a><br>
          <a class=menu href="http://music.bw.org/" title="Original Music by Bill Weinman">Bill&rsquo;s Music</a><br>
          <a class=menu href="http://whois.bw.org/">BW Whois</a><br>
          <a class=menu href="http://bw.org/ube/boulder.html">Boulder Pledge</a><br>
          <a class=menu href="http://bw.org/ube/" title="UBE-Related (Anti-Spam) Work">UBE-Related</a><br>
          <a class=menu href="http://blog.bw.org/" title="Bill&rsquo;s Blog">Blog</a><br>
          <a class=menu href="http://cgi.bw.org/" title="Bill&rsquo;s Simple CGI Scripts">CGI Scripts</a><br>
          <a class=menu href="http://cms.bw.org/" title="Content Management System">CMS Project</a><br>
          <a class=menu href="http://webmusicdb.com/" title="The Web Music Database (webmusicdb.com)">Music DB</a><br>
          <a class=menu href="http://htmlbook.com/" title="Creative HTML Design">Creative HTML</a><br>
          <a class=menu href="http://cgibook.com/">The CGI Book</a><br>
          <a class=menu href="http://perlbook.com/" title="Bill&rsquo;s New Perl Book (in progress)">Perl Book</a><br>
          <a class=menu href="http://www.weinman.com/wew/" title="Bill&rsquo;s original splash page">BillyDos</a><br>
          <a class=menu href="http://bw.org/privacy.html" title="Privacy Statement">Privacy</a><br>
          <a class=menu href="http://bw.org/end/" title="The end of the Internet">The End</a><br>
          <table cellpadding=0 cellspacing=0 border=0>  <!-- vertical spacer -->
             <tr><td height=5></td></tr></table> 
        </td></tr></table></td></tr>
      </table>
      </td></tr></table>



<table cellpadding=0 cellspacing=0 border=0><tr><td height=5></td><tr></table>

<!-- paypal donation button -->
<table cellpadding=0 cellspacing=0 border=0><tr><td bgcolor=black>
<table cellpadding=2 cellspacing=2 border=0><tr><td bgcolor=white>
  <form action="https://www.paypal.com/cgi-bin/webscr" method="post">
  <input type="hidden" name="cmd" value="_xclick">
  <input type="hidden" name="business" value="opensource@bw.org">
  <input type="hidden" name="item_name" value="BW Open Source Donation">
  <input type="hidden" name="no_shipping" value="1">
  <input type="hidden" name="return" value="https://bw.org/donation-thankyou.html">
  <input type="hidden" name="cancel_return" value="https://bw.org/">
  <input type="image" vspace=2 hspace=5 align=left src="https://i.bw.org/bw/paypal-donate.gif" border="0" name="submit" 
    alt="Make payments with PayPal - it's fast, free and secure!">
  </form>
</td></tr></table>
</td></tr></table>
<!-- end paypal donation button -->



<table cellpadding=0 cellspacing=0 border=0><tr><td height=5></td><tr></table>

<!-- Sponsored Links -->

  <table cellpadding=0 cellspacing=0 border=0 width=100><tr><td bgcolor=white>
  <table cellpadding=0 cellspacing=1 border=0>
    <tr><td width=100 bgcolor=black>
    <table width="100%" cellpadding=0 cellspacing=2 border=0>
    <tr><td bgcolor=black width="100%" align=center>
      <font face="tahoma,verdana,helvetica,arial" size=2 color=white>
      <b><a href="http://bw.org/donate.html" class="menu-title">&middot; Sponsors &middot; </a></b>
      </font>
    </td></tr>
    <tr><td bgcolor=white width="100%" align=center>

    <table cellpadding=0 cellspacing=0 border=0>
    <tr><td height=5></td></tr>

    <tr><td align=center class="textad"><a class="textad" target="_blank" 
      href="http://bw.org/u/ldc00">lynda.com video tutorials</a>

    <tr><td align=center class="textad"><a class="textad" target="_blank" 
      href="http://www.amazon.com/?_encoding=UTF8&tag=bw-org-20">amazon.com</a>

    <tr><td align=center class="textad"><a class="textad" target="_blank" 
      href="http://www.ConqueringArthritis.com/">Rheumatoid Arthritis</a></td></tr>

    <td height=5></td><tr>
    </table>

    </td></tr></table></td></tr>
  </table>
  </td></tr></table>

<!-- end Sponsored Links -->



<table cellpadding=0 cellspacing=0 border=0><tr><td height=5></td><tr></table>

<table width=100 cellpadding=0 cellspacing=0 border=0><tr><td align=center>
<table cellpadding=0 cellspacing=0 border=0><tr><td bgcolor=white>
<table cellpadding=0 cellspacing=1 border=0>
  <tr><td bgcolor=black>
    <table cellpadding=0 cellspacing=2 border=0 width="100%">
      <tr><td bgcolor=white align=center>
        <a href="https://bw.org/"><img src="https://i.bw.org/bw/bw-designed-by.gif"
          width=100 height=26 border=0 
          alt="Site Design: Bill Weinman" Title="Site Design: Bill Weinman"></a></td></tr>
    </table>
  </td></tr>
</table>
</td></tr></table>
</td></tr></table>

<table cellpadding=0 cellspacing=0 border=0><tr><td height=10></td><tr></table>

<div class="outer">
<div id="copyright">
    <p>
        &copy;&nbsp;1972&ndash;2018 <a href="http://bhg.bw.org/" class="no-highlight">BHG&nbsp;LLC</a>
    </p>
</div>
</div>


  </td>
  <td width=20><img src="https://i.bw.org/bw/blank.gif" width=20 height=1 border=0></td> <!-- space between columns --> 

  <td id="mainBody" width=668 align=left valign=top>


<p id="updated">
    updated 16 December 2014

</p>

<div id="socialMedia">
<p class="small text" style="text-align: center"> Connect with Bill </p>
<p>
<a href="https://bw.org/u/fb01" target="_blank" title="Facebook"><img 
    src="https://bw.org/images/icons/Facebook-24x24.png" width="24" height="24" border="0" alt="Facebook"></a>
<a href="https://bw.org/u/li01" target="_blank" title="Linked In"><img 
    src="https://bw.org/images/icons/Linked-In-24x24.png" width="24" height="24" border="0" alt="Linked In"></a>
<a href="https://bw.org/u/tw01" target="_blank" title="Twiter Feed"><img 
    src="https://bw.org/images/icons/Twitter-24x24.png" width="24" height="24" border="0" alt="Twitter Feed"></a><br/>
</p></div>


<h1 id="heading"> Bill Weinman </h1>

<p class="first">
Bill Weinman is a programmer, author, musician, and technologist, in no particular order. 
See Bill's <a href="bio.html">biography</a> and his <a href="resume/">r&eacute;sum&eacute;/<span style="font-size: 85%">CV</span></a> for more information. 
</p>

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<h2>
<a href="/u/ldc00" class="noshade" target="_blank">lynda.com</a>
Courses
<span class="small">[<a class="noshade" href="/ldcfaq/">FAQ</a>]</a>
</h2>

<p>
  Bill is currently writing and delivering online courses for
  <a href="/u/lynda.com">lynda.com</a>,
  the 
  <a href="/u/lynda.com">premier source for online training.</a>
  Some of his courses include:
</p>

<ul>
    <li> <a href="http://u.bw.org/ldc-cpp" target="_blank">C++ Essential Training</a> <span class="small highlight">NEW! December 2014</span> </li>
    <li> <a href="http://u.bw.org/ldc-cppcc" target="_blank">C++ Code Clinic</a> <span class="small highlight">NEW! July 2014</span> </li>
    <li> <a href="http://u.bw.org/ldc-mysql2014" target="_blank">MySQL Essential Training</a> <span class="small highlight">NEW! May 2014</span> </li>
    <li> <a href="http://u.bw.org/ldc-sql2014" target="_blank">SQL Essential Training</a> <span class="small highlight">NEW! March 2014</span> </li>
    <li> <a href="http://u.bw.org/ldc-iossys" target="_blank">iOS 6: iOS System Resources</a> <span class="small">August 2013</span> </li>
    <li> <a href="http://u.bw.org/ldc-x4esst" target="_blank">Xcode 4 Essential Training</a> <span class="small">March 2013</span> </li>
    <li> <a href="http://u.bw.org/ldc-iossql" target="_blank">iOS SDK and SQLite: Building Data-Driven Apps</a> <span class="small">January 2013</span> </li>
    <li> <a href="http://u.bw.org/ldc-h5e12" target="_blank">HTML Essential Training</a> <span class="small ">September 2012</span> </li>
    <li> <a href="http://u.bw.org/ldc-h5msg" target="_blank">HTML5: Messaging and Communications in Depth</a> <span class="small">January 2012</span> </li>
    <li> <a href="http://u.bw.org/ldc-docedit" target="_blank">HTML5: Document Editing in Depth</a> <span class="small">January 2012</span> </li>
    <li> <a href="http://u.bw.org/ldc-h5workers" target="_blank">HTML5: Background Processing with Web Workers</a> <span class="small">January 2012</span> </li>
    <li> <a href="http://u.bw.org/ldc-pgsql" target="_blank">PostgreSQL 9 with PHP Essential Training</a> <span class="small">November 2011</span> </li>
    <li> <a href="http://u.bw.org/ldc-h5dnd" target="_blank">HTML5: Drag and Drop in Depth</a> <span class="small">July 2011</span> </li>
    <li> <a href="http://u.bw.org/ldc-h5ls" target="_blank">HTML5: Local Storage and Offline Applications in Depth</a> <span class="small">June 2011</span> </li>
    <li> <a href="http://u.bw.org/ldc-iosstore" target="_blank">Distributing iOS Applications Through the App Store</a> <span class="small">Feb 2011</span> </li>
    <li> <a href="http://u.bw.org/ldc-macstore" target="_blank">Distributing Mac OSX Applications Through the App Store</a> <span class="small">Feb 2011</span> </li>
    <li> <a href="http://u.bw.org/ldc-ios4data" target="_blank">iOS SDK 4: Building Data-Driven Applications </a> <span class="small">Dec 2010</span> </li>
    <li> <a href="http://u.bw.org/ldc-sqlite3esst" target="_blank">SQLite 3 with PHP Essential Training</a> <span class="small ">Oct 2010</span> </li>
    <li> <a href="http://u.bw.org/ldc-python3esst" target="_blank">Python 3 Essential Training</a>  <span class="small "> Aug 2010 </span> </li>
    <li> <a href="http://u.bw.org/ldc-perl5esst" target="_blank">Perl 5 Essential Training</a> <span class="small"> Apr 2010 </span> </li>
    <li> <a href="http://u.bw.org/ldc-css4dev" target="_blank">CSS For Developers</a> <span class="small">Feb 2010</span> </li>
    <li> <a href="http://u.bw.org/ldc-cgiesst" target="_blank">CGI Essential Training</a> <span class="small">Jan 2010</span> </li>
    <li> <a href="http://u.bw.org/ldc-dynamenus" target="_blank">Creating Dynamic Menus</a> <span class="small">Dec 2009</span> </li>
    <li> <a href="http://u.bw.org/ldc-css" target="_blank">CSS Positioning</a> <span class="small">Aug 2009</span> </li>
    <li> <a href="http://u.bw.org/ldc-mysql" target="_blank">MySQL Essential Training</a> <span class="small">2009</span>  </li>
    <li> <a href="http://u.bw.org/ldc-xhtml" target="_blank">XHTML/HTML Essential Training</a> <span class="small">2009</span> </li>
    <li> <a href="http://u.bw.org/ldc-sql" target="_blank">SQL Essential Training</a> <span class="small">2009</span> </li>
    <li> <a href="http://u.bw.org/ldc-spam" target="_blank">Managing Spam Essential Training</a> <span class="small">2008</span> </li>
</ul>

<p>
    If you have questions or comments about any of Bill's courses on lynda.com, please read the
    <a href="/ldcfaq/">lynda.com FAQ</a>
    before
    <a href="/contact/">writing to him</a>
    about them. 
</p>

<h2>
    <a href="http://bhg.bw.org/" class="noshade" target="_blank">Contract Programming</a>
</h2>

<p>
    After more than 30 years of working on long-term projects Bill has shifted his focus to
    smaller jobs to better support his writing and open-source projects. 
</p>
<p>
    Please feel free to <a href="/contact/">contact Bill</a> with your small project needs. 
</p>

<h2>
    <a href="http://whois.bw.org/" class="noshade" target="_blank">BW Whois</a>
</h2>

<p>
    <a href="http://whois.bw.org/" target="_blank">BW Whois</a> is Bill's open-source 
    whois client. Originally released in December 1999, and still in active development,
    BW Whois has evolved into a full-featured
    command-line/web client with rich security features, caching and database support.
</p>

<h2>
    <a class="noshade" href="/books/" target="_blank">Books and Writings</a>
</h2>

<p> 
Mr. Weinman has written five books, including
<a href="http://www.cgibook.com/" target="_blank">The CGI Book</a> and,
with his sister <a href="/u/ldc-lynda" target="_blank">Lynda</a>,
<a href="http://www.htmlbook.com/" target=_blank>Creative HTML Design</a>.
He has contributed to other books on programming and web design and has written articles 
for various computer-related periodicals. Recently his writing has been focused on 
developing courseware for <a href="/u/ldc00 " target="_blank">lynda.com</a>.
</p>

<h2>
    <a href="http://amtp.bw.org/" class="noshade" target="_blank">AMTP</a>
</h2>

<p> 
<a href="http://amtp.bw.org/" target="_blank">AMTP</a>
(Authenticated Mail Transfer Protocol) is Bill's solution to the SPAM problem. 
See the 
<a href="http://amtp.bw.org/" target="_blank">AMTP web site</a>
for more information. 
</p>

<h2>
    <a href="http://music.bw.org/" class="noshade" target="_blank">Bill's Music</a>
</h2>

<p>
    Bill is an extremely talented guitarist and composer. While he has been focused 
    on non-music pursuits of late, you can always hear and download his music 
    <a href="http://music.bw.org/" target="_blank">here</a>. 
</p>

<h2>
    <a href="http://bearheart.wordpress.com/" class="noshade" target="_blank">BearHeart</a>
</h2>

<p>
    BearHeart is Bill's spiritual alter-ego. He is studying native american shamanic medicine 
    and has aspirations of becoming a teacher in the 
    <a href="http://www.dtmms.org/" target="_blank">Sweet Medicine Sundance</a> path. 
    BearHeart has recently begun a <a href="http://bearheart.wordpress.com/" target="_blank">blog</a>. 
</p>

<h2>
    <a href="http://blog.bw.org/" class="noshade" target="_blank">Blog</a>
</h2>

<p> Bill occasionally scribbles in his 
<a href="http://blog.bw.org/" target="_blank">blog</a>. 
</p>

<p class=small> <u>NOTE</u>: Because of Bill's
<a href="http://whois.bw.org/">bw-whois</a> program, some people seem 
to think that he has some control over the registration of domains. Unless you are a 
client or a personal friend, Bill 
<a href="http://whois.bw.org/registration-issues.html">does not</a>
have anything to do with your domain so please 
do not write to him about it (and please do not call him at home about it!) 
He cannot help you, and due to the surprisingly large volume of requests, he probably will not answer your message. 
</small>


    </td></tr>
    <tr><td colspan=2></td><td height=40 align=center valign=middle>
      <table cellpadding=0 cellspacing=0 border=0>
        <tr><td height=25></td></tr>
        <tr><td bgcolor="#999999" height=1></td></tr>
        <tr><td align=center class="small">Eezz beeg trouble for moose and squirrel.</td></tr>
        <tr><td height=15></td></tr>
        <tr><td align=center class="small">At BHG Worldwide Headquarters it is now six till two, on Wednesday, 22 August 2018.
</td></tr>
        <tr><td height=15></td></tr>
        <tr><td align="center"><img src="https://i.bw.org/bw/yy-31.png"
          width="31" height="31" alt="&middot;/." title="&middot;/."></td></tr>
      </table>
    </td></tr>
</table>
</body>
</html>

import random

print(random.randint(1, 1000))

564
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]

x = list(range(25))
print(x)
random.shuffle(x)
print(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
[23, 4, 15, 8, 5, 24, 7, 9, 10, 19, 22, 21, 1, 17, 0, 6, 3, 12, 18, 11, 14, 16, 13, 2, 20]

import datetime
now = datetime.datetime.now()
print(now)
2017-06-07 18:25:55.802692

print(now.year, now.month, now.day)
2017 6 7

conditions

i = 2

if i == 2:
    print('it is number two')
elif i % 2 == 0:
    print('it is also an even number')
else:
    print('do not know')
it is number two

i = 2

if i == 2:
    print('it is number two')
if i % 2 == 0:
    print('it is also an even number')
if i != 2:
    print('do not know')
it is number two
it is also an even number