Python Cheat Sheet 🏷️

# Creating variables (no type declaration needed)
name = "John"        # String
age = 25              # Integer
height = 5.9          # Float
is_student = True     # Boolean

print(name)           # → John
print(age)            # → 25

# Valid variable names
my_var = 10
myVar = 10
MyVar = 10
_private = 10
var123 = 10

# Invalid variable names (will cause errors)
# 123var = 10        # Cannot start with number
# my-var = 10        # Cannot contain hyphens
# my var = 10        # Cannot contain spaces

# Assign same value to multiple variables
a = b = c = 5
print(a, b, c)       # → 5 5 5

# Unpack values
x, y, z = 1, 2, 3
print(x, y, z)       # → 1 2 3

# Swap variables
x, y = y, x
print(x, y)          # → 2 1

# Global variable
global_var = 10

def my_function():
    # Local variable
    local_var = 5
    print(local_var)   # → 5
    print(global_var)  # → 10

my_function()
print(global_var)      # → 10
# print(local_var)     # Error: not defined outside function

age = 18

if age >= 18:
    print("Adult")
# Output: Adult

age = 15

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

score = 75

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
else:
    print("F")
# Output: C

age = 25
has_license = True

# AND operator
if age >= 18 and has_license:
    print("Can drive")
# Output: Can drive

# OR operator
if age < 18 or not has_license:
    print("Cannot drive")

# NOT operator
if not (age < 18):
    print("Is adult")
# Output: Is adult

i = 0
while i < 3:
    print(i)
    i += 1
# Output: 0, 1, 2

i = 0
while i < 10:
    if i == 3:
        break  # Exit loop
    print(i)
    i += 1
# Output: 0, 1, 2

i = 0
while i < 5:
    i += 1
    if i == 2:
        continue  # Skip this iteration
    print(i)
# Output: 1, 3, 4, 5

for i in range(3):
    print(i)
# Output: 0, 1, 2

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)
# Output: apple, banana, cherry

fruits = ["apple", "banana", "cherry"]

for i, fruit in enumerate(fruits):
    print(i, fruit)
# Output: 0 apple, 1 banana, 2 cherry

# range(start, stop, step)
for i in range(0, 10, 2):
    print(i)
# Output: 0, 2, 4, 6, 8

for i in range(5):
    if i == 3:
        break
    print(i)
# Output: 0, 1, 2

for i in range(5):
    if i == 2:
        continue
    print(i)
# Output: 0, 1, 3, 4

for i in range(3):
    for j in range(2):
        print(f"i={i}, j={j}")

# Output:
# i=0, j=0
# i=0, j=1
# i=1, j=0
# i=1, j=1
# i=2, j=0
# i=2, j=1

# Integer to Float
x = 10
y = 5.5
z = x + y
print(z)        # → 15.5 (float)
print(type(z))  # → <class 'float'>

# From string
num_str = "42"
num_int = int(num_str)
print(num_int)      # → 42

# From float (truncates decimal)
num_float = 3.9
num_int = int(num_float)
print(num_int)      # → 3

# From boolean
bool_val = True
num_int = int(bool_val)
print(num_int)      # → 1

# From string
num_str = "3.14"
num_float = float(num_str)
print(num_float)    # → 3.14

# From integer
num_int = 42
num_float = float(num_int)
print(num_float)    # → 42.0

# From boolean
bool_val = False
num_float = float(bool_val)
print(num_float)    # → 0.0

# From number
num = 42
str_num = str(num)
print(str_num)      # → "42"

# From float
num_float = 3.14
str_num = str(num_float)
print(str_num)      # → "3.14"

# From boolean
bool_val = True
str_bool = str(bool_val)
print(str_bool)     # → "True"

# From number
print(bool(1))        # → True
print(bool(0))        # → False
print(bool(5))        # → True

# From string
print(bool("hello"))  # → True
print(bool(""))       # → False (empty string)

# From list
print(bool([1, 2]))   # → True
print(bool([]))       # → False (empty list)

# From string
str_val = "abc"
list_val = list(str_val)
print(list_val)      # → ['a', 'b', 'c']

# From tuple
tuple_val = (1, 2, 3)
list_val = list(tuple_val)
print(list_val)      # → [1, 2, 3]

# From range
range_val = range(3)
list_val = list(range_val)
print(list_val)      # → [0, 1, 2]

# From list
list_val = [1, 2, 3]
tuple_val = tuple(list_val)
print(tuple_val)     # → (1, 2, 3)

# From string
str_val = "abc"
tuple_val = tuple(str_val)
print(tuple_val)     # → ('a', 'b', 'c')

abs(-5)              # Absolute value → 5
round(3.14159, 2)    # Round to 2 decimals → 3.14
max(1, 5, 3)         # Maximum value → 5
min(1, 5, 3)         # Minimum value → 1
sum([1, 2, 3, 4])    # Sum of list → 10
pow(2, 3)            # Power (2^3) → 8
len([1, 2, 3])       # Length of list → 3

int("5")             # String to integer → 5
float("3.14")        # String to decimal → 3.14
str(42)              # Number to string → "42"
bool(1)              # To boolean → True

list("abc")          # String to list → ['a', 'b', 'c']
tuple([1, 2, 3])     # List to tuple → (1, 2, 3)
dict([("a", 1)])     # List of tuples to dict → {'a': 1}

range(5)                      # Create sequence → 0, 1, 2, 3, 4
enumerate(["a", "b"])       # Get index and value
zip([1, 2], ["a", "b"])     # Combine lists → (1, 'a'), (2, 'b')
sorted([3, 1, 2])             # Sort items → [1, 2, 3]
list(reversed([1, 2, 3]))     # Reverse items → [3, 2, 1]

print()               # Print output to screen
input("Enter: ")      # Get user input

type(5)               # Get data type → <class 'int'>
isinstance(5, int)    # Check if type matches → True

all([True, True])     # All items True? → True
any([False, True])    # Any item True? → True

import math

# Square root and power
math.sqrt(16)        # Square root → 4.0
math.pow(2, 3)       # Power (2^3) → 8.0

# Rounding
math.ceil(3.14)      # Round up → 4
math.floor(3.14)     # Round down → 3

# Trigonometry
math.sin(0)          # Sine of angle
math.cos(0)          # Cosine of angle
math.tan(0)          # Tangent of angle

# Logarithm and exponential
math.log(10)         # Natural logarithm
math.exp(2)          # e raised to power x

# Constants
math.pi              # Pi → 3.14159...
math.e               # Euler's number → 2.71828...

text = "hello"

# Change case
text.upper()                 # → "HELLO"
text.lower()                 # → "hello"

# Find and replace
text.replace("l", "L")      # → "heLLo"
"hello".find("l")           # → 2
"hello".count("l")          # → 2

text = "hello world"

# Split string into list
text.split()                 # → ['hello', 'world']
"a,b,c".split(",")           # → ['a', 'b', 'c']
"Hello, World!".split(", ")  # → ['Hello', 'World!']

# Join list into string
" ".join(["hello", "world"])  # → "hello world"
",".join(["a", "b", "c"])    # → "a,b,c"

text = "  hello  "

text.strip()         # Remove both sides → "hello"
text.lstrip()        # Remove left side only → "hello  "
text.rstrip()        # Remove right side only → "  hello"

text = "Hello"

text[0]              # First character → "H"
text[-1]             # Last character → "o"
text[1:4]            # Characters 1-3 → "ell"
text[0:3]            # First 3 characters → "Hel"

arr = [1, 2, 3]

# Access elements
arr[0]               # First element → 1
arr[-1]              # Last element → 3
arr[0:2]             # Slice: elements 0-1 → [1, 2]

# Get info
len(arr)             # Length → 3

arr = [1, 2, 3]

arr.append(4)        # Add to end → [1, 2, 3, 4]
arr.insert(0, 0)     # Insert at index 0 → [0, 1, 2, 3, 4]

arr = [0, 1, 2, 3, 4]

arr.pop(0)           # Remove at index 0, returns 0
arr.remove(2)        # Remove by value

mapping = {"a": 1, "b": 2}

# Access values
mapping["a"]         # By key → 1
mapping.get("a")      # Safe access → 1
mapping.get("c", 0)   # Default if not found → 0

# Check if exists
"a" in mapping        # Is key in dict? → True

mapping = {"a": 1, "b": 2}

mapping.keys()        # → dict_keys(['a', 'b'])
mapping.values()      # → dict_values([1, 2])
mapping.items()       # → dict_items([('a', 1), ('b', 2)])

len(mapping)          # Number of items → 2

text = "Hello, World!"

# Step 1: Split on comma
words = text.split(",")
print(words)  # ['Hello', ' World!']

# Step 2: Remove spaces from each element
words = [s.strip() for s in words]
print(words)  # ['Hello', 'World!']

# Step 3: Join with space
result = " ".join(words)
print(result)  # 'Hello World!'

arr = [10, 20, 30]

for i, v in enumerate(arr):
    print(i, v)

# Output:
# 0 10
# 1 20
# 2 30

mapping = {1: True, 2: False, 3: True}

if 100 in mapping:
    print("100 is in mapping")
elif 2 in mapping:
    print("2 is in mapping")
else:
    print("Neither 100 nor 2 is in mapping")

from datetime import date, datetime

now = datetime.now()
print(now)  # → 2026-03-09 14:30:45.123456

today = date.today()
print(today)  # → 2026-03-09

current_time = datetime.now().time()
print(current_time)  # → 14:30:45.123456

from datetime import datetime

now = datetime.now()

print(now.year)    # → 2026
print(now.month)   # → 3
print(now.day)     # → 9
print(now.hour)    # → 14
print(now.minute)  # → 30
print(now.second)  # → 45

from datetime import date

d = date(2026, 3, 9)
print(d)  # → 2026-03-09

print(d.weekday())       # → 0 (Monday=0, Sunday=6)
print(d.strftime("%A"))  # → Monday

from datetime import datetime

dt = datetime(2026, 3, 9, 14, 30, 45)
print(dt)  # → 2026-03-09 14:30:45

from datetime import datetime

now = datetime.now()

# Common format codes:
# %Y = Year (4 digits) → 2026
# %y = Year (2 digits) → 26
# %m = Month (01-12) → 03
# %d = Day (01-31) → 09
# %H = Hour (00-23) → 14
# %M = Minute (00-59) → 30
# %S = Second (00-59) → 45
# %A = Full weekday name → Monday
# %a = Short weekday name → Mon
# %B = Full month name → March
# %b = Short month name → Mar

print(now.strftime("%Y-%m-%d"))
print(now.strftime("%H:%M:%S"))
print(now.strftime("%A, %B %d, %Y"))
print(now.strftime("%d/%m/%Y"))
print(now.strftime("%m/%d/%Y %H:%M:%S"))

from datetime import datetime

date_str = "2026-03-09"
dt = datetime.strptime(date_str, "%Y-%m-%d")
print(dt)  # → 2026-03-09 00:00:00

datetime_str = "03/09/2026 14:30:45"
dt = datetime.strptime(datetime_str, "%m/%d/%Y %H:%M:%S")
print(dt)  # → 2026-03-09 14:30:45

from datetime import datetime, timedelta

now = datetime.now()

future = now + timedelta(days=7)
print(future)

past = now - timedelta(days=7)
print(past)

diff = future - past
print(diff.days)  # → 14

from datetime import datetime, timedelta

now = datetime.now()

future_hours = now + timedelta(hours=5)
future_minutes = now + timedelta(minutes=30)
future_seconds = now + timedelta(seconds=45)
future_combined = now + timedelta(days=1, hours=5, minutes=30, seconds=45)

print(future_hours)
print(future_minutes)
print(future_seconds)
print(future_combined)

from datetime import datetime

date1 = datetime(2026, 3, 1)
date2 = datetime(2026, 3, 9)

diff = date2 - date1
print(diff.days)            # → 8
print(diff.total_seconds()) # → 691200.0

from datetime import datetime, timezone

utc_time = datetime.now(timezone.utc)
print(utc_time)  # → 2026-03-09 14:30:45.123456+00:00

local_time = datetime.now()
print(local_time)  # → 2026-03-09 14:30:45.123456

import time

start = time.time()

for _ in range(1_000_000):
    pass

end = time.time()
elapsed = end - start
print(f"Elapsed time: {elapsed:.2f} seconds")

import time

print("Start")
time.sleep(2)
print("After 2 seconds")

from collections import deque

queue = deque()

queue.append(1)
queue.append(2)
queue.append(3)
# Queue now: deque([1, 2, 3])

item = queue.popleft()
print(item)   # → 1
print(queue)  # → deque([2, 3])

if queue:
    print("Queue has items")

len(queue)  # → 2

import heapq

heap = []

heapq.heappush(heap, 5)
heapq.heappush(heap, 3)
heapq.heappush(heap, 7)
heapq.heappush(heap, 1)

print(heap)  # → [1, 3, 7, 5]

min_val = heap[0]
print(min_val)  # → 1

min_val = heapq.heappop(heap)
print(min_val)  # → 1
print(heap)     # → [3, 5, 7]

nums = [5, 3, 7, 1]
heapq.heapify(nums)
print(nums)  # → [1, 3, 7, 5]

max_heap = []
heapq.heappush(max_heap, -5)
heapq.heappush(max_heap, -3)

max_val = -heapq.heappop(max_heap)
print(max_val)  # → 5

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

head = Node(1)
head.next = Node(2)
head.next.next = Node(3)

current = head
while current:
    print(current.data, end=" -> ")
    current = current.next
print("None")

new_node = Node(0)
new_node.next = head
head = new_node

current = head
while current.next:
    current = current.next
current.next = Node(4)

head = head.next
print(head.data)  # → 1

def reverse_linked_list(head):
    prev = None
    current = head
    while current:
        next_temp = current.next
        current.next = prev
        prev = current
        current = next_temp
    return prev

head = reverse_linked_list(head)

graph = {
    "A": ["B", "C"],
    "B": ["A", "D"],
    "C": ["A", "E"],
    "D": ["B", "F"],
    "E": ["C", "F"],
    "F": ["D", "E"],
}

from collections import deque

def bfs(graph, start):
    visited = set()
    queue = deque([start])
    visited.add(start)

    while queue:
        node = queue.popleft()
        print(node, end=" ")

        for neighbor in graph[node]:
            if neighbor not in visited:
                visited.add(neighbor)
                queue.append(neighbor)
    print()

bfs(graph, "A")  # Output: A B C D E F

def dfs(graph, start, visited=None):
    if visited is None:
        visited = set()

    visited.add(start)
    print(start, end=" ")

    for neighbor in graph[start]:
        if neighbor not in visited:
            dfs(graph, neighbor, visited)

dfs(graph, "A")  # Output: A B D F E C

from collections import deque

def shortest_path(graph, start, end):
    visited = set()
    queue = deque([(start, [start])])

    while queue:
        node, path = queue.popleft()

        if node == end:
            return path

        if node not in visited:
            visited.add(node)

            for neighbor in graph[node]:
                if neighbor not in visited:
                    queue.append((neighbor, path + [neighbor]))

    return None

path = shortest_path(graph, "A", "F")
print(path)

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
]

print(matrix[0][0])  # → 1
print(matrix[1][1])  # → 5
print(matrix[2][2])  # → 9

matrix[0][0] = 10

rows = len(matrix)
cols = len(matrix[0])

for i in range(rows):
    for j in range(cols):
        print(matrix[i][j], end=" ")
    print()

for j in range(cols):
    for i in range(rows):
        print(matrix[i][j], end=" ")
    print()

transposed = [[matrix[i][j] for i in range(rows)] for j in range(cols)]
print(transposed)

rotated = [[matrix[rows - 1 - j][i] for j in range(cols)] for i in range(rows)]
print(rotated)

total = sum(sum(row) for row in matrix)
print(total)

def find_in_matrix(matrix, target):
    for i in range(len(matrix)):
        for j in range(len(matrix[0])):
            if matrix[i][j] == target:
                return (i, j)
    return None

position = find_in_matrix(matrix, 5)
print(position)  # → (1, 1)

n, m = 3, 4
matrix = [[0 for _ in range(m)] for _ in range(n)]
print(matrix)

def greet():
    print("Hello!")

greet()  # → Hello!

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

result = add(5, 3)
print(result)  # → 8

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

greet()         # → Hello, Guest!
greet("John")   # → Hello, John!

def get_coordinates():
    return 10, 20

x, y = get_coordinates()
print(x, y)  # → 10 20

def sum_all(*args):
    return sum(args)

print(sum_all(1, 2, 3, 4))  # → 10

def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

print_info(name="John", age=25)

try:
    num = int("abc")
except ValueError:
    print("Invalid number")

try:
    x = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")
except ValueError:
    print("Invalid value")

try:
    with open("data.txt", "r") as file:
        data = file.read()
except FileNotFoundError:
    print("File not found")
else:
    print(data)
finally:
    print("Done")

try:
    result = 10 / 0
except Exception as e:
    print(f"Error: {e}")

with open("data.txt", "r") as file:
    content = file.read()
    print(content)

with open("data.txt", "r") as file:
    for line in file:
        print(line.strip())

with open("data.txt", "w") as file:
    file.write("Hello, World!")

with open("data.txt", "a") as file:
    file.write("\nNew line")

lines = ["Line 1", "Line 2", "Line 3"]
with open("data.txt", "w") as file:
    file.writelines([line + "\n" for line in lines])

with open("data.txt", "r") as file:
    lines = file.readlines()
    print(lines)

squares = []
for i in range(5):
    squares.append(i ** 2)

squares = [i ** 2 for i in range(5)]
print(squares)  # → [0, 1, 4, 9, 16]

evens = [i for i in range(10) if i % 2 == 0]
print(evens)  # → [0, 2, 4, 6, 8]

nums = [int(x) for x in ["1", "2", "3"]]
print(nums)  # → [1, 2, 3]

matrix = [[i + j for j in range(3)] for i in range(3)]
print(matrix)

add = lambda x, y: x + y
print(add(5, 3))  # → 8

square = lambda x: x ** 2
print(square(4))  # → 16

nums = [1, 2, 3, 4]
squared = list(map(lambda x: x ** 2, nums))
print(squared)  # → [1, 4, 9, 16]

nums = [1, 2, 3, 4, 5, 6]
evens = list(filter(lambda x: x % 2 == 0, nums))
print(evens)  # → [2, 4, 6]

students = [("John", 25), ("Jane", 23), ("Bob", 24)]
sorted_by_age = sorted(students, key=lambda x: x[1])
print(sorted_by_age)

s = {1, 2, 3, 3, 2}
print(s)  # → {1, 2, 3}

s = set([1, 2, 3])
print(s)  # → {1, 2, 3}

s = {1, 2, 3}

s.add(4)
s.remove(2)
s.pop()

print(1 in s)
print(len(s))

s1 = {1, 2, 3}
s2 = {2, 3, 4}

print(s1 | s2)  # Union → {1, 2, 3, 4}
print(s1 & s2)  # Intersection → {2, 3}
print(s1 - s2)  # Difference → {1}

name = "John"
age = 25

print(f"Name: {name}, Age: {age}")
print(f"Result: {10 + 5}")

name = "John"
age = 25

print("Name: {}, Age: {}".format(name, age))
print("Name: {0}, Age: {1}".format(name, age))

name = "John"
age = 25

print("Name: %s, Age: %d" % (name, age))

num = 3.14159

print(f"{num:.2f}")
print(f"{num:>10}")
print(f"{1000:,}")

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

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

dog = Dog("Buddy")
dog.bark()

class Car:
    wheels = 4

    def __init__(self, brand):
        self.brand = brand

    def drive(self):
        print(f"{self.brand} is driving")

car = Car("Toyota")
print(car.wheels)
car.drive()

class Animal:
    def sound(self):
        print("Generic sound")

class Dog(Animal):
    def sound(self):
        print("Woof!")

dog = Dog()
dog.sound()

import math

print(math.sqrt(16))  # → 4.0

from math import pi

print(pi)  # → 3.14159...

import numpy as np
import pandas as pd

from datetime import datetime, timedelta

now = datetime.now()
future = now + timedelta(days=7)
print(future)

# save as utils.py
def add(a, b):
    return a + b

# In another file
from utils import add

print(add(5, 3))  # → 8