PCAP

Use of imports

import pandas as pd
from pandas import DataFrame as Frame

Importing a module is done by an instruction named import.
A module is identified by its name.
Each module consistis of entities (functions, variables, constants, classes and objects).

Given the function:

def add(a, b):
    result = a + b
    return

The call add(3, 5) will result in None.

LEGB is the rule by which Python resolves names. The letters in LEGB stand for Local, Enclosing, Global and Built-in scope.

The code:

from builtins import sum


print(sum([4, 6]))


def sum(iterable):
    result = 0
    for item in iterable:
        result += item * 2
    return result


print(sum([4, 6]))

will result in:
10
20

KeyError is raised when a mapping (dictionary) key is not found in the set of existing keys.
','.join(list_name) returns a string which is the concatenation of the strings of list_name.
Method Resolution Order (MRO) is the order in which base classes are searched for a member during lookup.
list.index(x[, start[, end]]) - return zero-based index in the list of the first item whose value is equal to x. Raises a ValueError if there is no such item.

The following dictionaries are given:

stocks_1 = {'MSFT': 280.0, 'AAPL': 146.39, 'TSLA': 644.22}
stocks_2 = {'AMZN': 3573.0, 'NVDA': 726.44}

You can combine them with:

stocks_1 | stocks2 
stocks_1.update(stocks2) 
{**stocks_1, **stocks2}

help([object]) - invokes the built-in help system.
Convert a list to a set and back to a list again to remove duplicates from the list.
The try/except statement specifies exception handlers and/or cleanup code for a group of statements.
A docstring is a string literal that occurs as the first statement in a module, function, class, or method definition. Such a docstring becomes the __doc__ special attribute of that object.

The following reverse list:

[IN]: numbers = list(range(10, 100, 10))
[IN]: numbers[::-1]
[OUT]: [90, 80, 70, 60, 50, 40, 30, 20, 10]

The following reverse list and return every second element:

[IN]: numbers = list(range(10, 100, 10)) <br>
[IN]: numbers[::-2] <br>
[OUT]: [90, 70, 50, 30, 10]

Variable name cannot start with a digit.
Space character is not allowed in a variable name

The following code will result in data not received

data_stream = ''
while data_stream:
    print('data received')
else:
    print('data not received')

Python is a high level programming language.
Protected members of a class are accessible from within the class and are also available to its sub-classes. No other environment is permitted access to it. This enables specific resources of the parent class to be inherited by the child class. Python's convention to make an instance variable protected is to add a prefix _ (single underscore) to it.
The meaning of the keyword argument is determined by its name specified along with its value.
Guido van Rossum is the creator of Python.

The following answers will create an empty class

class Company(object):
    pass

class Company: pass

class Company:
    pass

pip list - Lists installed packages, including editables. Packages are listed in a case-insensitive sorted order.
pip freeze - outputs installed packages in requirements format. Packages are listed in a case-insensitive sorted order.
bin(x) - convert an integer number to a binary string prefixed with “0b”.
Considering p = Person() you get class name using type(p).__name__ and p.__class__.__name__.
from math import * is usnafe. You will import all entities from math module.
__file__ - the pathname of the file from which the module was loaded, if it was loaded from a file.

The following code:

    a = [1, 2, 3, 4, 5]
    b = a
    b[:] = [3, 6]

will result in:

b = [3, 6]
a = [3, 6]

You only need to add a double underscore __ before the attribute name to make it private.
Assert statements are a convenient way to insert debugging assertions into a program.
Function definition must be placed before the first invocation.
list() is list() is false because there two different lists.
str.title() - return a titlecased version of the string where words start with an uppercase character and the remaining characters are lowercase.
from math import sin, exp - It's correct, but not recommended due to stylistic reasons. It's better and prettier to express the same intention in more a verbose and explicit form using two lines.
issubset(other) or set <= other - test whether every element in the set is in other.
True and and are reserved words in Python.
A docstring is a string literal that occurs as the first statement in a module, function, class, or method definition. Such a docstring becomes the __doc__ special attribute of that object.

The following commands will check the pip version:

pip --version
python -m pip --version
py -m pip --version

Special attributes of the classes:
- __name__ - the class name
- __module__ - the name of the module in which the class was defined
- __dict__ - the dictionary containing the class’s namespace
- __bases__ - a tuple containing the base classes, in the order of their occurrence in the base class list
- __dict__ - the dictionary containing the class’s namespace
- __annotations__ - a dictionary containing variable annotations collected during class body execution.
[*list1, *list2] - combine two lists.
The __init__.py files are required to make Python treat directories containing the file as packages.
Both are correct:
```
import os
import sys
```
```
import os, sys
```

Both are incorrect:

from python import os
from python import sys

from python import os, sys

isinstance(object, classinfo) - return True if the object argument is an instance of the classinfo argument.

Note the increment_age method.

class Pet:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def increment_age(self):
        self.age += 1

hasattr(object, name) - the arguments are an object and a string. The result is True if the string is the name of one of the object’s attributes, False if not.
pip show - Show information about one or more installed packages. The output is in RFC-compliant mail header format.
str.splitlines(keepends=False) - returns a list of the lines in the string, breaking at line boundaries.
Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language and first released it in 1991 as Python 0.9.0.
List than contains None value can not be sorted.

Using the code:

from machine_learning import classification_report

you can use:

classification_report()

Python 3.6 introduced underscores in numeric literals, which allows you to place single underscores between numbers and after base specifiers to improve readability. This feature is not available in older Python versions.
Yield expressions and statements are only used when defining a generator function, and are only used in the body of the generator function.
NameError is raised when a local or global name is not found.
PSF - Python Software Foundation.
Python’s default arguments are evaluated once when the function is defined, not each time the function is called.
The following declarations are valid:
```
a, b = 'a', 'b'
a = 'a'; b = 'b'
```
repr(object) - return a string containing a printable representation of an object.

The following code is valid:

try:
    import my_package
except ModuleNotFoundError as err:
    print(err)

Break ouside loop will raise a SyntaxError exception.

All the declarations are valid:

stocks1 = ('AAPL',)
stocks2 = tuple(['AAPL'])
stocks3 = 'AAPL',

In Python, all exceptions must be instances of a class that derives from BaseException.
str.strip([chars]) - returns a copy of the string with the leading and trailing characters removed.
str.rstrip([chars]) - returns a copy of the string with trailing characters removed.
str.lstrip([chars]) - returns a copy of the string with leading characters removed.

How to delete the code:

course_name = 'python interview'

del course_name
del globals()['course_name']
del(course_name)

The pass statement does nothing. It can be used when a statement is required syntactically but the program requires no action.
hasattr(object, name) - the arguments are an object and a string. The result is True if the string is the name of one of the object’s attributes, False if not.
Multiline strings, which occupy more than one line of source code are delimited by trigraphs:
- '''
- """
List comprehensions provide a concise way to create lists.
pip uninstall - Uninstall packages. pip is able to uninstall most installed packages.
Dictionaries keep the insertion order since Python 3.7 or higher.
The right argument of the % operator can not be zero.
issubclass(class, classinfo) - return True if class is a subclass (direct, indirect, or virtual) of classinfo.
An except clause may name multiple exceptions as a parenthesized tuple, for example:
```
except (RuntimeError, TypeError, NameError):
    pass
```
When iterating over a dictionary, we iterate over its keys by default.
id(object) - return the “identity” of an object.
numbers[:] is a copy of numbers = [1, 2,3]
True + True + 2 * True - False = 4
There is no switch statement in Python.
object.__new__(cls[, ...]) - called to create a new instance of class cls.
filter(function, iterable) - constructs an iterator from those elements of iterable for which function returns true.
ZeroDivisionError is raised when the second argument of a division or modulo operation is zero.
List slicing: list[start:stop:step]
pip freeze - outputs installed packages in requirements format. Packages are listed in a case-insensitive sorted order.

The code:

input_str = '3.14'
converted_int_number = int(input_str)

will raise ValueError exception.

0., .0 and 1e6 are float types.
iterator - an object representing a stream of data. Repeated calls to the iterator’s __next__() method (or passing it to the built-in function next()) return successive items in the stream. Iterators are required to have an __iter__() method that returns the iterator object itself
ord(c) - given a string representing one Unicode character, return an integer representing the Unicode code point of that character.
Use the global to create a global variable from local scope.
The compiled Python bytecode is stored in files which have their names ending with pyc.
PEP stands for Python Enhancement Proposal. The PEP is a design document that provides information to the Python community or describes a new Python function, its processes, or its environment. It is also a set of rules that determine how Python code is formatted for maximum readability.
zip(*iterables, strict=False) - iterate over several iterables in parallel, producing tuples with an item from each one.
sys.version - a string containing the version number of the Python interpreter plus additional information on the build number and compiler used.
any(iterable) - return True if any element of the iterable is true. If the iterable is empty, return False.
builtins module provides direct access to all ‘built-in’ identifiers of Python; for example, builtins.open is the full name for the built-in function open().
Python strings are immutable.
A special method (magic method) is a method that is implicitly called by Python to perform a specific operation. For example, such as addition, subtraction, extended assignment, etc. Special methods have names that begin and end with double underscores.
PEP8 is a document that provides coding conventions and style guide for Python code.
importlib.reload(module) - reloads a previously imported module.
PyPI is shor for Python Package Index.
When a Python source file is imported for the first time, a __pycache__ directory will be created in the package directory, if one does not already exist.
You cannot append elements to tuples.
var = 36e-4 -> 0.0036
'python' * False = ''
var1 is var2 = true if they have the same value.
When a dictionary is converted to a set using set() the result is a set of dictionary keys.
The datetime module supplies classes for manipulating dates and times.
An infinite recursive function will raise RecursionError exception.
class type(name, bases, dict, **kwds) - with one argument, return the type of an object.
Conda and Pip are package managers.
CPython is the default implementation of the Python programming language.
Python While Else - With the else statement we can run a block of code once when the condition no longer is true:
Python supports functional programming.
object.__repr__(self) - called by the repr() built-in function to compute the “official” string representation of an object.
SyntaxError is raised when the parser encounters a syntax error.
keyword.kwlist - sequence containing all the keywords defined for the interpreter.
do while is not available in Python.
Lambda function has a : as example:
```
lambda (a,b): True
```
true does not exist. True is correct.
re module in Python supports regular expressions.
10 != '1' + '0' results in True. No exception is raised.
The platform.system() function returns a string with your OS name, the platform.version() function returns a string with your OS version. The platform.processor() function returns a string with the name of your processor.
os.mkdir("a/b/c/d") will raise FileExistsError if d exists.
The integer value of True is 1.
If the index is given, pop() removes and returns the element at the given index.
When there is no __str__() method present and you print an object, Python shows the object id in that way.
insert(0, 1) inserts 1 before index 0 (at the front of the list).
break can not be used outside of a loop, and the default except must be last.

The values that become False in Python are the following:

print(bool(''))        # False
print(bool(0))         # False
print(bool(0.0))       # False
print(bool(0j))        # False
print(bool(None))      # False
print(bool([]))        # False
print(bool(()))        # False
print(bool({}))        # False
print(bool(set()))     # False
print(bool(range(0)))  # False

The Exception class contains a property named args and it is a tuple.
First use pip list --outdated to list your outdated packages. Then use pip install -U package_name to update one of the packages.
The read() method reads the whole content of a file and returns it as a string. The readline() method only reads one line. The readlines() method also reads the whole content but returns it as a list of lines.
If a variable name shadows into a function you can use it in an expression or you can assign a new value to it BUT you can not do both at the same time.
The division operator ALWAYS returns a float.
An imported module is executed only once.
range(-1, -2) has no element.
If you have instance variables with two leading underscores, you can not just access them from outside of the class. The code will raise AttributeError exception.
The digraph written as #! is used to tell a Unix or Unix-like OS how to execute the contents of a Python file.
List slicing: [start(inclusive):end(exclusive):step]
ZeroDivisionError is a subclass of ArithmeticError.
Python Package Index is also known as the Cheese Shop
stdin, stdout, stderr are names of pre-opened streams.
stdout and stderr are associated with the console.
stdin is associated with the keyboard.
A list of package's dependencies can be obtained from pip using its command named show.
String literals that are delimited by whitespace are automatically concatenated.
Lambda functions can have any number of arguments but only one expression.
__eq__() overloads the equal to operator.
errno.ENOENT symbol refers to an error described as No such file or directory.
None value can not be used as an argument of arithmetic operators.
from x.y import z causes the import of entity z from module y from package x.
default 'except:' must be last
A code point is a number which makes up a character.
listdir() never includes the special entries . and ..
The math.floor() method rounds a number DOWN to the nearest integer.
The math.ceil() method rounds a number UP to the nearest integer.
The tuple.index() method expects a value and looks for that value in the tuple. It will return the index of the first value it finds. If it does not find the value, it raises a ValueError.
The method in Python to immediately terminate a program is sys.exit().
A string is immutable. You can not change it. You can read something by indexing, BUT you can not write something by indexing.
A source file named __init__.py is used to mark a directory/folder as containing a Python package, and to initialize the package.
'' in 'alphabet' is True.
Pip means Pip Installs Packages.
The pyc files are created by the Python interpreter when a py file is imported. They contain the compiled bytecode of the imported module.
Greater than operator and less than operator have the highest precedence. The logical and operator has a higher precedence than the logical or operator.
Imported files get executed only once.
The list of possible exceptions has to be in parentheses.
Every object has the method __len__(). Normally we use the function len() which calls the method __len__().
The folder created by Python used to store pyc files is named __pycache__.
The rfind() method finds the last occurrence of a specified value.
The index() method finds the first occurrence of a specified value.
print('is' in 'This IS Python code.') is True.
A string is immutable and if you create two strings with the same value they will both point to the same object and therefore have the same ids.
In range(start, end) The start value has to be lower than the end value. Otherwise range() does not return an element.
A tuple can be the index of a dictionary.
Packages can contain modules.
Since Python 3.4 pip has been included with the Python installer.
If both operands are an integer the floor division operator will return an integer. If at least one operand is a float the result will also be a float.
In the list of classes to inherit from a superclass cannot come before its subclass.
The dir() function returns the names of all entities (properties and methods) of the passed module (or object).
Dictionary can have different data types as a key. BUT if an integer and a float have the same value, the second value overrides the first values.
The isdigit() method checks if all the characters in the string are digits.
If you try to divide by a string you get a TypeError.
If a class doesn't define its own constructor, the constructor of its superclass is invoked.
Error is not a subclass of RuntimeError.

The code:

def func(data):
    data = [7, 23, 42]
    print('Function scope: ', data)


data = ['Peter', 'Paul', 'Mary']
func(data)
print('Outer scope: ', data)

will print:

Function scope: [7, 23, 42]
'Outer scope: ['Peter', 'Paul', 'Mary']

The read() method has one optional parameter. If it is given, that number of characters are read.
There is no increment operator ++ in Python. You can add as many plus signs as you like, the number stays positive.

The output of the code:

for i in range(1):
    print('*')
else:
    print('*')

will be:

**

The print() function called without an argument will print an empty line. The amount of possible arguments depends on the capacities of your computerbut it is going to be more than you will ever need.
The empty string is smaller than any other.
pip --version and pip -V will show pip version.
The read() function reads the whole file and returns a string. The readlines() function also reads the whole file and returns a list of the single lines. And you can also iterate through the file object. In each iteration you will get one line.
at mode will allow you to append text in a file.

edgarpf/pcap

PCAP