FREE Python 3 Cheatsheet | Quick Reference | PDF

Python is one of the most widely-used languages today, with immense and ever-growing popularity. It has gained recognition for its large role in machine learning and AI, but Python has various applications in many other fields, including data science, cybersecurity, game development, app development, backend development and so on. Some of the most popular libraries in these fields and others include Pandas, Numy, Pytorch, Tensorflow, Flask, Django, and countless others.

This cheatsheet was made to be as concise as possible while covering some of the core syntax of python. It is example-based, so everything is given in the form of working code.

Whether you are just starting out as a developer, or have extensive experience, this cheatsheet will help you to understand and recall the fundamentals of Python 🔥🐍

Download as PDF

Strings
Lists
Dictionaries
Sets
Loops and Control Flow
Modules
Files
Exceptions
Functions
OOP

Strings

# Multiline strings
multiline_string = """This is a
multiline string"""

# Length of a string
length = len("Hello")  # Output: 5

# Checking if a string starts with a specific substring
starts_with = "Hello, World".startswith("Hello")  # Output: True

# Checking if a string ends with a specific substring
ends_with = "Hello, World".endswith("World")  # Output: True

# String interpolation
name = "Alice"
age = 30
message = f"My name is {name} and I am {age} years old."

# String formatting
formatted_message = "My name is {} and I am {} years old.".format(name, age)

# Replacing substrings in a string
new_string = "Hello, World".replace("World", "Python")  # Output: Hello, Python

# Splitting a string into a list of substrings
words = "Hello, World".split(",")  # Output: ['Hello', ' World']

# Splicing a string
spliced_string = "Hello, World"[1:5]  # Output: "ello"

# Converting a string to lowercase
lowercase_string = "Hello".lower()  # Output: "hello"

# Converting a string to title case
title_case_string = "hello world".title()  # Output: "Hello World"

# Splitting a string into lines
lines = "Hello\nWorld".splitlines()  # Output: ['Hello', 'World']

Lists

# Creating a list
my_list = list(range(1, 6))  # Output: [1, 2, 3, 4, 5]

# Slicing a list
sliced_list = my_list[1:4]  # Output: [2, 3, 4]

# Length of a list
length = len(my_list)  # Output: 5

# Sum of all elements in a list
total = sum(my_list)  # Output: 15

# Minimum value in a list
minimum = min(my_list)  # Output: 1

# Maximum value in a list
maximum = max(my_list)  # Output: 5

# Appending an element to a list
my_list.append(6)  # Output: [1, 2, 3, 4, 5, 6]

# Sorting a list
my_list.sort()  # Output: [1, 2, 3, 4, 5, 6]

# Joining list elements into a string
joined_string = ", ".join(map(str, my_list))  # Output: "1, 2, 3, 4, 5, 6"

# List comprehensions
squared = [x**2 for x in my_list]  # Output: [1, 4, 9, 16, 25, 36]

# Removing an element from a list by value
my_list.remove(3)  # Output: [1, 2, 4, 5, 6]

# Reversing a list
reversed_list = my_list[::-1]  # Output: [6, 5, 4, 2, 1]

Dictionaries

# Creating a dictionary
my_dict = {'a': 1, 'b': 2, 'c': 3}

# Accessing values using keys
value = my_dict['a']  # Output: 1

# Getting all keys
keys = my_dict.keys()  # Output: dict_keys(['a', 'b', 'c'])

# Getting all values
values = my_dict.values()  # Output: dict_values([1, 2, 3])

# Getting key-value pairs as tuples
items = my_dict.items()  # Output: dict_items([('a', 1), ('b', 2), ('c', 3)])

# Enumerating through dictionary items
for index, (key, value) in enumerate(my_dict.items()):
print(index, key, value)

Sets

# Creating a set
my_set = {1, 2, 3}

# Set operations (union, intersection, difference)
union_set = {1, 2, 3} | {3, 4, 5}  # Output: {1, 2, 3, 4, 5}
intersection_set = {1, 2, 3} & {3, 4, 5}  # Output: {3}
difference_set = {1, 2, 3} - {3, 4, 5}  # Output: {1, 2}

Loops and Control Flow

# If statement
x = 10
if x > 5:
print("x is greater than 5")
elif x == 5:
print("x is equal to 5")
else:
print("x is less than 5")

# While loop
x = 0
while x < 5:
print(x)
x += 1
if x == 3:
continue  # Skip the rest of the loop body and continue with the next iteration
if x == 4:
break  # Exit the loop completely

# For loop
for i in range(5):
print(i)

Modules

# Importing a module
import math

# Importing specific names from a module
from math import pi

Files

# Opening a file
file = open("filename.txt", "r")

# Reading from a file
content = file.read()

# Writing to a file
with open("filename.txt", "w") as file:
file.write("Hello, world!")

Exceptions

# Exception handling
try:
result = 10 / 0
except ZeroDivisionError as e:
print("Error:", e)

Functions

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

result = add(3, 4)  # Output: 7

# default values (default values in function parameters)
def greet(name="World"):
print("Hello, " + name)

greet()  # Output: Hello, World
greet("Alice")  # Output: Hello, Alice

# keyword arguments
def greet_with_age(name, age):
print(f"Hello, {name}! You are {age} years old.")

greet_with_age(name="Alice", age=30)  # Output: Hello, Alice! You are 30 years old.

# docstrings (docstrings for documenting functions)
def multiply(a, b):
"""
This function multiplies two numbers.
"""
return a * b

# *args (arbitrary number of arguments)
def add(*args):
total = 0
for num in args:
total += num
return total

result = add(1, 2, 3, 4)  # Output: 10

# **kwargs (arbitrary number of keyword arguments)
def greet_with_details(**kwargs):
if 'name' in kwargs and 'age' in kwargs:
print(f"Hello, {kwargs['name']}! You are {kwargs['age']} years old.")
else:
print("Hello, Unknown!")

greet_with_details(name="Alice", age=30)  # Output: Hello, Alice! You are 30 years old.


# Taking command line arguments
import sys

def main():
# Taking command line arguments
if len(sys.argv) == 3:
arg1 = int(sys.argv[1])
arg2 = int(sys.argv[2])
print(f"Result: {arg1 + arg2}")
else:
print("Usage: python script.py <arg1> <arg2>")

if __name__ == "__main__":
main()

OOP (Object-Oriented Programming)

# Class initialization
class MyClass:
def __init__(self, x):
self.x = x

def print_x(self):
print(self.x)

# Defining a method inside a class
class MyClass:
def my_method(self):
pass

# Using class methods
class MyClass:
    @classmethod
def my_class_method(cls):
pass

# Inheritance
class ChildClass(ParentClass):
pass