wdonet/python-basis

python-basis

• Python is an interpreted language

• The interpreter and the extensive standard library are freely available from Python Web Site (https://www.python.org/)

• The interpreter is easily extended with new functions and data types implemented in C and C++

• Simpler than Java or C/C++ and more powerful than unix shell script or Windows batch files

• More error checking than C

• Python allows to split the program into modules, standard modules includes:

  • I/O
  • System calls
  • Sockets
  • UI

• Comparing to Java and C++

  • The high-level data types allows to express complex operations in a single statement
  • Statements grouping is done by indentation instead of beginning and ending brackets
  • No variable or arguments declarations are necessary

• Python standard library: https://docs.python.org/3/library/index.html#library-index

Dev environment setup

1. Download and install python 3.6 from: https://www.python.org/downloads/mac-osx/
2. It is usually installed on /usr/local/bin/python3.6
3. After installed it can be invoked in command line by typing python3.6
4. To exit the prompt type: Control-D or type quit()
5. It is not necessary an IDE but some helpful IDEs can be:
   • PyCharm (Idea)
   • Netbeans
   • Eclipse

Files encoding

By default files are treated as encoded in UTF-8

Python sintax

Comments

Comments starts with the hash character (#) and extend to the end of the physical line

Operators

Arithmetic

• Plus +
• Minus -
• Multiply *
• Classic division /
• Floor division //
• Reminder %
• Power **
• Assignment =
• In interactive mode the last printed expression is assigned to variable "_"
• In addition to int and float python supports Decimal and Fraction and has built in support for complex numbers and uses j or J to indicate the imaginary part.

Boolean operators

• and
• or
• not

Comparisons

• Less than <
• Less than or equal <=
• Greater than >
• Greater than or equal >=
• Equal ==
• Not equal !=
• Object identity is
• Negated object identity is not

Bitwise operators

• Or |
• X-or ^
• And &
• Shift left <<
• Shift right >>
• Invert bits ~

More about data types: https://docs.python.org/3/library/stdtypes.html

Strings

• Strings are enclosed in single quotes or double quotes with the same meaning
• Special characters are escaped with backslashes
• Raw strings are preceded by character r (r'Some string'), and using those ones escaped characters are not interpreted
• Concatenation is achieved using + operator
• Strings can be repeated using * operator
• Characters in string can be indexed using [] operator, being the first character 0-index
• It is possible to use negative indexes to start counting from the right
• Slicing is supported using [begin_index:end_index] begin included, end excluded
• Begin or end can be omitted
• Python strings are immutable
• String length is retrieved using built in function len

More information:

https://docs.python.org/3/library/stdtypes.html#textseq
https://docs.python.org/3/library/stdtypes.html#string-methods
https://docs.python.org/3/reference/lexical_analysis.html#f-strings
https://docs.python.org/3/library/string.html#formatstrings
https://docs.python.org/3/library/stdtypes.html#old-string-formatting

Lists

• Lists can be written as a sequence of comma separated values which can be different in type
  squares = [1, 4, 9, 16, 25]
• Lists can be indexed and sliced as strings
• Lists can be concatenated using +
• Lists are MUTABLE
• Using append method can be added new items to the list
• Assign to slice is also possible
• List length is retrieved using built in function len

Control flow

If statement

x = 10
if x < 0:
    print ('Negative value')
elif x == 0:
    print ('zero')
else:
    print('Positive value')

For statement

For each style

words = ['cat', 'window', 'defenestrate']
for w in words:
    print(w, len(w))

Using range

for i in range(5):
    print(i)

• For supports break and continue as in Java or C but adds support for else statement

Pass statements

pass statement does nothing. It can be used when a statement is required syntactically but the program requires no action

def new_function(parameter):
    pass

Functions

def new_function(parameter):
    return parameter

Default argument values

Keyword arguments

Arbitrary argument lists

Lambda expressions

Handling exceptions

def number(parameter):
    try:
        return int(parameter)
    except ValueError:
        return float(parameter)

Data structures

Lists

Tuples

Sequences

Sets

Dictionaries

Modules

Standard modules

Packages

Classes

https://docs.python.org/3/tutorial/classes.html

Coding style (PEP 8)

• Use 4-space indentation, and no tabs.
• Wrap lines so that they don’t exceed 79 characters.
• Use blank lines to separate functions and classes, and larger blocks of code inside functions.
• When possible, put comments on a line of their own.
• Use docstrings.
• Use spaces around operators and after commas, but not directly inside bracketing constructs: a = f(1, 2) + g(3, 4).
• Name your classes and functions consistently; the convention is to use CamelCase for classes and lower_case_with_underscores for functions and methods. Always use self as the name for the first method argument (see A First Look at Classes for more on classes and methods).
• Don’t use fancy encodings if your code is meant to be used in international environments. Python’s default, UTF-8, or even plain ASCII work best in any case.
• Likewise, don’t use non-ASCII characters in identifiers if there is only the slightest chance people speaking a different language will read or maintain the code.

Documentation strings

https://docs.python.org/3/tutorial/controlflow.html#documentation-strings

Installing python modules (pip)

python3.6 -m pip install SomePackage

https://docs.python.org/3/tutorial/venv.html#managing-packages-with-pip

Python unit tests

https://docs.python.org/3/library/unittest.html

References

https://docs.python.org/3/tutorial/ http://stackoverflow.com/questions/81584/what-ide-to-use-for-python https://docs.python.org/2/library/unittest.html