Python CheatSheet – A Quick Guide for Beginners & Developers

This Cheatsheet covers these all topic from basic to advance concept of Python

1. Basics

print("Hello, World!")

x, y = 10, 3.14
name = "Alice"
is_active = True

print(type(x))   # <class 'int'>

2. Data Types & Casting

int(), float(), str(), bool(), complex()

s = "Python"
print(s.lower(), s.upper(), s[::-1])  # reverse

3. Collections

# List
fruits = ["apple", "banana"]
fruits.append("mango")
fruits[0]

# Tuple
t = (1, 2, 3)

# Set
s = {1, 2, 2, 3}
s.add(4)

# Dictionary
person = {"name": "John", "age": 25}
person["city"] = "NY"

4. Operators

+, -, *, /, //, %, **    # arithmetic
==, !=, >, <, >=, <=     # comparison
and, or, not             # logical
in, not in               # membership

5. Conditionals & Loops

if x > 5:
    print("big")
elif x == 5:
    print("equal")
else:
    print("small")

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

while x > 0:
    x -= 1

6. Functions

def greet(name="Guest"):
    return f"Hello, {name}"

# Lambda
square = lambda n: n*n

# Comprehensions
evens = [x for x in range(10) if x % 2 == 0]

7. File Handling

with open("file.txt", "w") as f:
    f.write("Hello")

with open("file.txt", "r") as f:
    print(f.read())

8. Exceptions

try:
    x = 1/0
except ZeroDivisionError:
    print("Error!")
finally:
    print("Done")

9. OOP (Classes)

class Person:
    def __init__(self, name):
        self.name = name
    def greet(self):
        print(f"Hi, I’m {self.name}")

p = Person("Alice")
p.greet()

10. Modules & Pip

import math, random
print(math.sqrt(16), random.randint(1,10))

# Pip
# pip install requests

11. Decorators

def log(func):
    def wrapper(*args, **kwargs):
        print("Calling", func.__name__)
        return func(*args, **kwargs)
    return wrapper

@log
def hello():
    print("Hello")

hello()

12. Generators & Iterators

def countdown(n):
    while n > 0:
        yield n
        n -= 1

for num in countdown(5):
    print(num)

13. Context Managers

class MyFile:
    def __enter__(self): print("Open"); return self
    def __exit__(self, *args): print("Close")

with MyFile() as f:
    print("Inside")

14. Typing & Annotations

def add(x: int, y: int) -> int:
    return x + y

15. Dataclasses

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

p = Point(1,2)
print(p)

16. Async / Await

import asyncio

async def say_hi():
    print("Hi")
    await asyncio.sleep(1)
    print("Bye")

asyncio.run(say_hi())

17. Regex

import re
txt = "Python 3.12"
match = re.search(r"\d+\.\d+", txt)
print(match.group())   # "3.12"

18. Data Science Basics

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

arr = np.array([1,2,3])
df = pd.DataFrame({"A":[1,2], "B":[3,4]})
plt.plot([1,2,3],[4,5,6]); plt.show()

19. Database (SQLite)

import sqlite3
con = sqlite3.connect("test.db")
cur = con.cursor()
cur.execute("CREATE TABLE IF NOT EXISTS users(id INT, name TEXT)")
cur.execute("INSERT INTO users VALUES(1, 'Alice')")
con.commit()

20. Testing

import unittest

def add(x,y): return x+y

class TestMath(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2,3), 5)

unittest.main()

21. Web (Flask Example)

from flask import Flask
app = Flask(__name__)

@app.route("/")
def home():
    return "Hello Flask!"

if __name__ == "__main__":
    app.run()

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