Python Programming Language Cheatsheet

Python Programming Language — Complete Beginner Cheat Sheet

1. What Is Python?

Python is a high-level, interpreted programming language known for its simple syntax and readability.
It’s widely used for backend development, automation, data science, AI, scripting, and APIs.

Python focuses on writing less code and doing more work.

2. Installing Python

After installing Python, you can run code using:

python app.py

Python executes files line by line (no compilation step like Java).

3. Hello World

print("Hello World")

This prints text to the console.
Python does not require classes or main methods to start.

4. Variables

Variables store values in memory.

age = 25
name = "Sumit"
active = True

Python is dynamically typed, meaning you don’t declare data types.

5. Comments

Used to explain code.

# single line comment

Comments improve readability and maintenance.

6. Data Types

Common built-in types:

int     → whole numbers  
float   → decimal numbers  
str     → text  
bool    → True / False

Python automatically detects types.

7. Type Checking

type(age)

Returns the variable’s data type.

8. Type Casting

Convert one type into another.

int("5")
str(10)
float(3)

Used when reading user input or APIs.

9. Operators

Arithmetic

+  -  *  /  %

Comparison

==  !=  >  <  >=  <=

Logical

and  or  not

Operators perform calculations and conditions.

10. Input From User

name = input("Enter name: ")

Input always returns a string.

🟢 Control Flow

11. if / else

if age > 18:
    print("Adult")
else:
    print("Minor")

Used to make decisions.

Indentation is mandatory in Python.

12. elif

elif age == 18:

Used for multiple conditions.

13. Loops

Loops repeat code automatically.

for loop

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

Used when number of iterations is known.

while loop

while x < 5:

Runs while condition remains true.

14. break / continue

break     → exits loop  
continue  → skips current iteration

🧺 Collections

15. List

Ordered, changeable, allows duplicates.

nums = [1,2,3]

Used for storing multiple values.

16. Tuple

Ordered but immutable.

t = (1,2,3)

Used when data should not change.

17. Set

Unordered, no duplicates.

s = {1,2,3}

Used for uniqueness.

18. Dictionary

Key-value pairs.

user = {"name":"Sumit","age":25}

Used heavily in APIs and JSON.

19. Common Collection Methods

append()  
remove()  
pop()  
keys()  
values()  
items()

Manipulate collections.

🔧 Functions

20. Function Definition

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

Functions make code reusable.

21. Default Parameters

def greet(name="Guest"):

Used when argument is optional.

22. *args and **kwargs

Handle variable arguments.

def test(*args, **kwargs):

Used in frameworks.

23. Lambda Function

Short anonymous functions.

lambda a,b: a+b

Used with filters and maps.

🧱 OOP in Python

24. Class

Blueprint of objects.

class Car:

25. Object

Instance of class.

c = Car()

26. Constructor

Runs automatically on object creation.

def __init__(self):

27. self

Refers to current object.

Used to access variables and methods.

28. Inheritance

Child class inherits parent.

class B(A):

Promotes reuse.

29. Encapsulation

Protect data using underscores.

_name   (protected)  
__name  (private)

30. Polymorphism

Same method behaves differently.

Python supports dynamic polymorphism.

31. Abstraction

Hide implementation details using ABC module.

⚠ Error Handling

32. try / except

try:
except Exception:

Prevents program crash.

33. finally

Always executes.

34. Custom Exception

class MyError(Exception):

File Handling

35. Read File

open("a.txt","r")

36. Write File

open("a.txt","w")

37. with Statement

Automatically closes files.

with open() as f:

Modules & Packages

38. Import Module

import math

39. From Import

from math import sqrt

40. pip

Python package manager.

pip install requests

Multithreading

41. Threading

Runs tasks in parallel.

import threading

42. Async / Await

Used for non-blocking code.

async def func():

Common in APIs.

Database

43. SQLite / PostgreSQL / MySQL

Python connects using libraries:

sqlite3  
psycopg2  
mysql-connector

Virtual Environment

44. venv

Creates isolated environment.

python -m venv env

Prevents dependency conflicts.

Professional Python

45. Popular Frameworks

Django  
Flask  
FastAPI

Used for backend APIs.

46. Testing

unittest  
pytest

Ensures correctness.

47. Logging

Tracks application behavior.

import logging

48. Deployment

Docker  
Gunicorn  
Nginx  
Cloud

Used for production.

49. Advanced Topics

Decorators  
Generators  
Context Managers  
Microservices  
Celery  
Redis  
Kafka

Used in large systems.

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