Python Cheatsheets

Quick reference for Python syntax, built-in functions, and standard library.

Variables

Containers for storing data values. Python is dynamically typed.

name = "Python"
age = 30
height = 5.9
is_active = True

Operators

Symbols that perform operations on variables and values.

a + b
x - y
count += 1
x == y
x > y
x and y
not flag

Data Types

Core built-in data types in Python.

text = "Hello"
number = 42
pi = 3.14
is_valid = False
items = [1, 2, 3]
settings = {"theme": "dark"}

Comments

Notes in the code ignored by the interpreter.

# This is a single-line comment
"""
This is a
multi-line comment
"""

Data Structures

Lists

Ordered, mutable collections.

fruits = ["apple", "banana", "cherry"]
fruits.append("orange")

Dictionaries

Key-value mappings.

user = {"name": "Alice", "age": 25}
print(user["name"])

Tuples

Ordered, immutable collections.

coords = (10, 20)
x, y = coords

Sets

Unordered unique collections.

numbers = {1, 2, 3, 3}
print(numbers)

Control Flow

If / Else

Conditional execution blocks.

if score > 50:
    print("Pass")
elif score == 50:
    print("Borderline")
else:
    print("Fail")

While Loop

Looping until a condition becomes false.

while x < 5:
    print(x)
    x += 1

For Loop

Looping over iterable objects.

for item in [1, 2, 3]:
    print(item)

Match Case

Structural pattern matching.

match status:
    case 200:
        print("OK")
    case 404:
        print("Not Found")

Functions

Defining Functions

Creating reusable blocks of code.

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

Arguments

Default, keyword, and variable-length arguments.

def connect(host="localhost", port=8080):
    return host, port

def add(*nums):
    return sum(nums)

def config(**settings):
    return settings

Lambda

Anonymous small inline functions.

square = lambda x: x * x

Variable Scope

Local vs global variable access.

x = 10

def func():
    global x
    x = 20

Built In Functions

I/O Functions

Built-in functions for input/output operations.

# print()
print("Hello World")

# input()
name = input("Enter name: ")

# format()
msg = "Hello {}".format(name)

# open()
with open("file.txt", "r") as f:
    data = f.read()

Iterator & Loop Helpers

Functions for iteration and looping.

range(5)
list(enumerate(["a", "b"]))
list(zip([1,2], ["a","b"]))
list(map(str, [1, 2, 3]))
list(filter(lambda x: x > 2, [1, 2, 3]))

Conversion & Casting

Convert values between common types.

str(10)
int("5")
float("3.14")
bool(1)
list("abc")
tuple([1, 2])
dict([["a",1]])
set([1, 2, 2])

Data Utility Functions

Helpers to work with data and sequences.

len([1, 2, 3])
sum([1, 2, 3])
min([5, 2, 7])
max([5, 2, 7])
sorted([3, 1, 2])
list(reversed([1, 2, 3]))

Type & Introspection Functions

Inspect objects and types at runtime.

type(10)
isinstance(5, int)
id("hello")
dir([])
vars()

Modules And Imports

Imports

Import modules and reuse code.

import math
from math import sqrt
import os as operating_system

Creating Modules

Build your own modules.

# file: mymodule.py
def greet():
    print("Hello")

# usage
import mymodule
mymodule.greet()

Standard Library

Useful built-in modules.

import os
import sys
import json
import random
import datetime

Object Oriented Programming

Classes

Templates for creating objects.

class Person:
    def __init__(self, name):
        self.name = name

Inheritance

Deriving classes from existing ones.

class Student(Person):
    pass

Exceptions

Try Except

Handle runtime errors gracefully.

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

Custom Exceptions

Define user-defined exceptions.

class MyError(Exception):
    pass

File Handling

File Read/Write

Handling files in Python.

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

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

Advanced Python

List Comprehensions

Concise syntax for creating lists.

squares = [x*x for x in range(10)]
evens = [n for n in range(20) if n % 2 == 0]

Generators

Lazily evaluate sequences with yield.

def gen():
    yield 1
    yield 2

Standard Library

Datetime

Work with dates and times.

from datetime import datetime
now = datetime.now()

OS Module

Interact with the operating system.

import os
os.listdir()
os.getcwd()

Popular Libraries

NumPy Basics

Numerical computations with arrays.

import numpy as np
arr = np.array([1,2,3])

Pandas Basics

Data analysis with DataFrames.

import pandas as pd
df = pd.DataFrame({"a":[1,2],"b":[3,4]})

Web Development

Simple HTTP Server

Start a basic HTTP server using Python's built-in http.server module.

# Python 3 built-in HTTP server
# Start server in current directory
python3 -m http.server 8000

# Custom handler example
from http.server import SimpleHTTPRequestHandler, HTTPServer

class MyHandler(SimpleHTTPRequestHandler):
    pass

server = HTTPServer(("localhost", 8080), MyHandler)
server.serve_forever()

FastAPI Basics

Fast and modern Python framework for building APIs.

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello FastAPI"}

# Run using: uvicorn filename:app --reload

Requests Library

Make HTTP GET, POST, and other requests using Python.

import requests

# GET request
r = requests.get("https://api.example.com/data")
r.json()

# POST request
requests.post("https://api.example.com/post", json={"key": "value"})

WebSocket Basics (Python)

Simple WebSocket echo server using websockets module.

import asyncio
import websockets

async def echo(websocket):
    async for message in websocket:
        await websocket.send(f"Echo: {message}")

asyncio.run(websockets.serve(echo, "localhost", 8765))

Flask Basics

Minimal example for building REST APIs and web apps using Flask.

from flask import Flask, jsonify

app = Flask(__name__)

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

@app.route("/api/data")
def data():
    return jsonify({"message": "Hello API"})

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

Flask Template Rendering

Serve HTML templates using Flask and Jinja2.

# app.py
from flask import Flask, render_template
app = Flask(__name__)

@app.route("/")
def index():
    return render_template("index.html", name="Python")

# templates/index.html
# <h1>Hello {{ name }}</h1>

Simple JSON API in Python

Build a minimal API without external frameworks using http.server.

from http.server import BaseHTTPRequestHandler, HTTPServer
import json

class APIHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.send_header("Content-type", "application/json")
        self.end_headers()
        response = {"message": "Hello from JSON API"}
        self.wfile.write(json.dumps(response).encode())

server = HTTPServer(("localhost", 5000), APIHandler)
server.serve_forever()

Uvicorn & Gunicorn

Production server options for FastAPI/Flask.

# Start FastAPI app
uvicorn app:app --host 0.0.0.0 --port 8000 --reload

# Production with Gunicorn + Uvicorn workers
gunicorn app:app -w 4 -k uvicorn.workers.UvicornWorker

Python Cheatsheets

Quick reference for Python syntax, built-in functions, and standard library.

Python Basics

Variables

Containers for storing data values. Python is dynamically typed.

name = "Python"
age = 30
height = 5.9
is_active = True

Operators

Symbols that perform operations on variables and values.

a + b
x - y
count += 1
x == y
x > y
x and y
not flag

Data Types

Core built-in data types in Python.

text = "Hello"
number = 42
pi = 3.14
is_valid = False
items = [1, 2, 3]
settings = {"theme": "dark"}

Comments

Notes in the code ignored by the interpreter.

# This is a single-line comment
"""
This is a
multi-line comment
"""

Data Structures

Lists

Ordered, mutable collections.

fruits = ["apple", "banana", "cherry"]
fruits.append("orange")

Dictionaries

Key-value mappings.

user = {"name": "Alice", "age": 25}
print(user["name"])

Tuples

Ordered, immutable collections.

coords = (10, 20)
x, y = coords

Sets

Unordered unique collections.

numbers = {1, 2, 3, 3}
print(numbers)

Control Flow

If / Else

Conditional execution blocks.

if score > 50:
    print("Pass")
elif score == 50:
    print("Borderline")
else:
    print("Fail")

While Loop

Looping until a condition becomes false.

while x < 5:
    print(x)
    x += 1

For Loop

Looping over iterable objects.

for item in [1, 2, 3]:
    print(item)

Match Case

Structural pattern matching.

match status:
    case 200:
        print("OK")
    case 404:
        print("Not Found")

Functions

Defining Functions

Creating reusable blocks of code.

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

Arguments

Default, keyword, and variable-length arguments.

def connect(host="localhost", port=8080):
    return host, port

def add(*nums):
    return sum(nums)

def config(**settings):
    return settings

Lambda

Anonymous small inline functions.

square = lambda x: x * x

Variable Scope

Local vs global variable access.

x = 10

def func():
    global x
    x = 20

Built In Functions

I/O Functions

Built-in functions for input/output operations.

# print()
print("Hello World")

# input()
name = input("Enter name: ")

# format()
msg = "Hello {}".format(name)

# open()
with open("file.txt", "r") as f:
    data = f.read()

Iterator & Loop Helpers

Functions for iteration and looping.

range(5)
list(enumerate(["a", "b"]))
list(zip([1,2], ["a","b"]))
list(map(str, [1, 2, 3]))
list(filter(lambda x: x > 2, [1, 2, 3]))

Conversion & Casting

Convert values between common types.

str(10)
int("5")
float("3.14")
bool(1)
list("abc")
tuple([1, 2])
dict([["a",1]])
set([1, 2, 2])

Data Utility Functions

Helpers to work with data and sequences.

len([1, 2, 3])
sum([1, 2, 3])
min([5, 2, 7])
max([5, 2, 7])
sorted([3, 1, 2])
list(reversed([1, 2, 3]))

Type & Introspection Functions

Inspect objects and types at runtime.

type(10)
isinstance(5, int)
id("hello")
dir([])
vars()

Modules And Imports

Imports

Import modules and reuse code.

import math
from math import sqrt
import os as operating_system

Creating Modules

Build your own modules.

# file: mymodule.py
def greet():
    print("Hello")

# usage
import mymodule
mymodule.greet()

Standard Library

Useful built-in modules.

import os
import sys
import json
import random
import datetime

Object Oriented Programming

Classes

Templates for creating objects.

class Person:
    def __init__(self, name):
        self.name = name

Inheritance

Deriving classes from existing ones.

class Student(Person):
    pass

Exceptions

Try Except

Handle runtime errors gracefully.

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

Custom Exceptions

Define user-defined exceptions.

class MyError(Exception):
    pass

File Handling

File Read/Write

Handling files in Python.

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

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

Advanced Python

List Comprehensions

Concise syntax for creating lists.

squares = [x*x for x in range(10)]
evens = [n for n in range(20) if n % 2 == 0]

Generators

Lazily evaluate sequences with yield.

def gen():
    yield 1
    yield 2

Standard Library

Datetime

Work with dates and times.

from datetime import datetime
now = datetime.now()

OS Module

Interact with the operating system.

import os
os.listdir()
os.getcwd()

Popular Libraries

NumPy Basics

Numerical computations with arrays.

import numpy as np
arr = np.array([1,2,3])

Pandas Basics

Data analysis with DataFrames.

import pandas as pd
df = pd.DataFrame({"a":[1,2],"b":[3,4]})

Web Development

Simple HTTP Server

Start a basic HTTP server using Python's built-in http.server module.

# Python 3 built-in HTTP server
# Start server in current directory
python3 -m http.server 8000

# Custom handler example
from http.server import SimpleHTTPRequestHandler, HTTPServer

class MyHandler(SimpleHTTPRequestHandler):
    pass

server = HTTPServer(("localhost", 8080), MyHandler)
server.serve_forever()

FastAPI Basics

Fast and modern Python framework for building APIs.

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello FastAPI"}

# Run using: uvicorn filename:app --reload

Requests Library

Make HTTP GET, POST, and other requests using Python.

import requests

# GET request
r = requests.get("https://api.example.com/data")
r.json()

# POST request
requests.post("https://api.example.com/post", json={"key": "value"})

WebSocket Basics (Python)

Simple WebSocket echo server using websockets module.

import asyncio
import websockets

async def echo(websocket):
    async for message in websocket:
        await websocket.send(f"Echo: {message}")

asyncio.run(websockets.serve(echo, "localhost", 8765))

Flask Basics

Minimal example for building REST APIs and web apps using Flask.

from flask import Flask, jsonify

app = Flask(__name__)

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

@app.route("/api/data")
def data():
    return jsonify({"message": "Hello API"})

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

Flask Template Rendering

Serve HTML templates using Flask and Jinja2.

# app.py
from flask import Flask, render_template
app = Flask(__name__)

@app.route("/")
def index():
    return render_template("index.html", name="Python")

# templates/index.html
# <h1>Hello {{ name }}</h1>

Simple JSON API in Python

Build a minimal API without external frameworks using http.server.

from http.server import BaseHTTPRequestHandler, HTTPServer
import json

class APIHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.send_header("Content-type", "application/json")
        self.end_headers()
        response = {"message": "Hello from JSON API"}
        self.wfile.write(json.dumps(response).encode())

server = HTTPServer(("localhost", 5000), APIHandler)
server.serve_forever()

Uvicorn & Gunicorn

Production server options for FastAPI/Flask.

# Start FastAPI app
uvicorn app:app --host 0.0.0.0 --port 8000 --reload

# Production with Gunicorn + Uvicorn workers
gunicorn app:app -w 4 -k uvicorn.workers.UvicornWorker