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Introduction to Python

This is a really condensed cheat sheet to get introduced into python. This assumes we use python 3.x (Python 2 reaches end-of-life)



Windows / OSX:

Linux / WSL: sudo apt update && sudo apt install python3 python3-pip

I recommend using python3 as python 2.x will come into deprecation soon

Run Python

Running Python interactive shell : python3

  • Interactive shell allows you to input commands and test scripts without using a script file.

Running a Python script $ python ./

Python scripts have the .py extension

Installing more components using PIP

PIP is a package installer, it downloads and adds features to the current python installation

$ pip install module1 module2 : installs modules

$ pip install -u module2: updates a module

Note: On windows, PIP can't be called directly, it has to be called from python3 -m pip

Writing Python Scripts

Python scripts are text files with the extension .py. They can be edited using any text editor but you can use advanced editors such as Notepad++, Sublime Text or advanced IDEs such as Visual Studio Code or PyCharm. The latter have better features, code discovery and debug capabilities.

Imports Section

Imports modules reside at the beginning of the script file.

import my-module : imports all the module classes from the module my-module

from my-module import SomeClass, SomeOtherClass: imports only some of the module classes from my-module

Many libraries exist in standard python installations, but more can be installed using PIP (See later)

Python Syntax

Python is script language that is executed from top to bottom. every line contains one statement every statement has to terminate using a line return.

print("This is a statement")
print("This is another statement")
name = "foo"
print("My name is {}".format(foo))


Single Line Comments start with a #

Multi Line Comments start and end with a """

# Single Line Comment
print("blah") # Comments can be after a statement
# But not before a statement : print("blah")
This is a multi-line comment
and is pretty handy to avoid
using too many # symbols


Indentation in Python defines the scope of the code: for instance anything indented below an if statement will be part of the if condition scope.

if my_condition == True:
    # this instruction will be executed only if true
    print("this is true")
    # end if
# then, let's go back to our execution outside of the if
print("I always say that")


Variables are data storage for values that can be then modified, assigned, read and compared to other variables.

Variables can be assigned using the = equal operator (note that it is different from the == equality comparison operator)

Variables exist in the function scope where they are declared.

Variables are dynamically typed and their creation and assignment follows these rules:

name = "foo"            # a new variable and assigns it the string "foo"
surname = "bar"         # another variable and assigns is the string "bar"
name = "foo fighter"    # changes the name of the first variable
surname = name          # assigns the contents of name into surname
name = 1                # name changes type and now becomes an integer

def getYear():          # now we enter a function scope
    birth = 2019        # we create birth variable into the scope
    print(birth)        # prints '2019'
    #end function

print(birth)            # ERROR! birth does not exist here, as is was created in
                        # the getYear function scope


Functions can be defined using the def keyword, followed by the function name, then all the function parameters between parenthesis.

Calling a function is made by using the function name and passing its parameters between parenthesis. The types are not precised in the function prototype.

Functions can return any value during its execution or None if the execution ends by falling out of the scope of the function

def bestoftwo(a, b)
    if a == b :
        print("We are tied!")
    elif a > b :
        print("A is the Best ({})".format(a))
    else :
        print("B is the Best ({})".format(b))

best = bestoftwo(14,4)