The Python Programming Language

This article serves as brief documentation for the Python Programming Language. It is by no means comprehensive; for full documentation, refer to the official documentation here.

Introduction to Python §

My First Python Program §

To create a Python program, we will create a file with the .py extension. Then, in this file we add commands in Python that will be evaluated at runtime.

Below, we create our first program, the “Hello World” program!

# hello.py
print("Hello World!")

Python is a general purpose language, and finds a variety of usage across Computer Science due to its relative ease of use.

Running Python Programs §

Python is an interpreted language. This means that unlike other languages whose code must first be compiled into executable code, Python code is directly read and evaluated, line by line, by another program called an interpreter.

To run a Python program, we use it’s interpreter, python3.

python3 hello.py

Basic Python Concepts §

Typing in Python §

Python has the following language properties:

• Dynamically Typed: Type checking of variables is performed at run-time.
• Latently (Implicitly) Typed: Variable types are inferred by the compiler and do not need to be explicitly declared.

These paradigms increase Python’s ease of use!

Basic Python Program §

A basic Python program is given below.

'''
Multiline Comment
'''
# Single Line Comment
 
# Obtain 
 

Control Flow §

while, for, etc

Scoping §

'''
throws an error - we're defining a local a before 
defining it globally.
'''
a = 5
def f():
	a = 7
	global a
	a = a + 1
	print(a)

python does not let us modify global variables in local functions - enter the global keyword, which will let us declare a variable as a global variable / let us modify it.

a = 5
 
'''
throws an error
'''
def f():
	a = a + 1
	print(a)
 
'''
okay
'''
def g():
	global a
	a = a + 1
	print(a)

OOP in Python §

Python supports Object Orientated Programming

class Test:
	# Constructor
	def __init__(self, _a: int):
		self.a = _a
	
	# To String Method
	def __str__():
		...
		
	# Method
	def method(self):
		print("Method Ran!")

Objects have methods, python has an equivalent to the “null’ type (None)

Security vs convenience - as security increases, convenience decreases

Type Checking §

Type checking refers to the process of determining a variable’s type. This lets us perform checks on variables and functions, to ensure that the program is running as intended (and throw errors if it is not).

Typing can occur at various stages of a program.

• Dynamic Typing: The performing of type checking at run-time.
• Static Typing: The performing of type checking at compile-time.

Additionally, typing can either be done explicitly or implicitly:

• Manifest (Explicit) Typing refers to the need to explicitly tell the compiler the type of new variables. In manifest typing, types are associated with variables.
• Latent (Implicit) Typing refers to the lack of need to give a type to a variable (the compiler will infer) In latent typing, types are associated with values.