November 24, 2024 • Cheatsheet • 7 min read

Python Cheatsheet

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Jinansh
Jinansh
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Python Cheatsheet for Beginners

Table of Contents

  1. Introduction
  2. Basics
  3. Data Types
  4. Control Flow
  5. Functions
  6. Modules
  7. File Handling
  8. Object-Oriented Programming
  9. Error Handling
  10. Common Built-in Functions
  11. Advanced Topics

Introduction

Python is a high-level, versatile programming language known for its simplicity and readability. You can use Python for web development, data analysis, artificial intelligence, and much more.

Basics

Printing and Comments

Printing is used to display output:

print("Hello, World!")  # This prints Hello, World! to the screen

Comments are notes for the programmer and ignored by Python:

# This is a single-line comment

'''
This is a
multi-line comment
'''

Variables

Variables store data. You don’t need to specify the type of a variable.

x = 5         # Integer
y = 3.14      # Float
name = "John" # String
is_happy = True  # Boolean

# You can print variables like this:
print("Name:", name)

Rules for Variable Names

  • Must start with a letter or an underscore.
  • Can only contain letters, numbers, and underscores.
  • Case-sensitive (Name and name are different).

Input

The input function takes user input as a string:

user_name = input("What is your name? ")
print(f"Nice to meet you, {user_name}!")

Data Types

Python has several data types to store different kinds of data.

Numbers

a = 10      # Integer
b = 3.14    # Float
c = 2 + 3j  # Complex number

Strings

Strings are text data enclosed in quotes:

text = "Hello"
print(text.upper())  # Convert to uppercase
print(text[1])       # Access character at index 1

String Concatenation:

first = "Hello"
second = "World"
combined = first + " " + second
print(combined)

String Formatting:

name = "Alice"
age = 25
print(f"My name is {name} and I am {age} years old.")

Lists

Lists are ordered collections of items.

numbers = [1, 2, 3, 4]
print(numbers[0])    # Access first item
numbers.append(5)    # Add an item
numbers.pop()        # Remove last item
print(numbers)

Dictionaries

Dictionaries store data in key-value pairs.

person = {"name": "Alice", "age": 25}
print(person["name"])  # Access value by key
person["age"] = 26     # Update value
print(person)

Tuples

Tuples are immutable lists (cannot be changed after creation).

coordinates = (10, 20)
print(coordinates[0])

Sets

Sets are collections of unique items.

unique_items = {1, 2, 3, 2}
unique_items.add(4)
print(unique_items)  # Output: {1, 2, 3, 4}

Control Flow

Control flow determines the order in which code runs.

If-Else

age = 18
if age >= 18:
    print("You are an adult.")
elif age > 13:
    print("You are a teenager.")
else:
    print("You are a child.")

Loops

For Loop:

for i in range(5):
    print(i)  # Outputs 0, 1, 2, 3, 4

While Loop:

count = 0
while count < 5:
    print(count)
    count += 1

Functions

Functions group reusable code.

Defining Functions

def greet(name):
    return f"Hello, {name}!"
print(greet("Alice"))

Default Parameters

def greet(name="stranger"):
    return f"Hello, {name}!"
print(greet())  # Outputs: Hello, stranger!

Modules

Modules are libraries of code you can import.

Importing Modules

import math
print(math.sqrt(16))

Installing External Modules

Use pip to install libraries:

pip install requests

File Handling

Reading and Writing Files

# Write to a file
with open("example.txt", "w") as file:
    file.write("Hello, file!")

# Read from a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

Object-Oriented Programming

OOP allows you to model real-world things using classes and objects.

Classes and Objects

class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed

    def bark(self):
        return f"{self.name} says Woof!"

dog = Dog("Buddy", "Golden Retriever")
print(dog.bark())

Error Handling

Handle errors gracefully with try-except blocks.

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"Error: {e}")
finally:
    print("Done!")

Common Built-in Functions

Math Functions

max([1, 2, 3])  # Find max
min([1, 2, 3])  # Find min
abs(-10)        # Absolute value
sum([1, 2, 3])  # Sum of elements

String Functions

len("hello")          # String length
"hello".replace("e", "a")  # Replace characters

Advanced Topics

List Comprehensions

squares = [x**2 for x in range(5)]
print(squares)

Lambda Functions

double = lambda x: x * 2
print(double(5))

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