name = "Alice"          # string
age = 30                # int
price = 9.99            # float
active = True           # bool
items = None            # NoneType
Multiple assignment
x, y, z = 1, 2, 3
a = b = c = 0
Type checking
type(name)              # <class ‘str’>
isinstance(age, int)    # True

name = "Alice"
age = 30
f”Hello, {name}!”                    # Hello, Alice!
f”{name} is {age} years old”         # Alice is 30 years old
f”{price:.2f}”                       # 9.99 (2 decimal places)
f”{1000000:,}”                       # 1,000,000
f”{‘hello’:>10}”                     # ’     hello’ (right-align)
f”{‘hello’:^10}”                     # ’  hello   ’ (center)
f”{name!r}”                          # ‘Alice’ (with quotes)

s = "Hello, World!"
s.lower()               # “hello, world!”
s.upper()               # “HELLO, WORLD!”
s.strip()               # remove whitespace from both ends
s.split(”, ”)           # [“Hello”, “World!”]
s.replace(“World”, “Python”)  # “Hello, Python!”
s.startswith(“Hello”)   # True
s.endswith(”!”)         # True
s.find(“World”)         # 7 (index, -1 if not found)
s.count(“l”)            # 3
”  “.join([“a”, “b”])   # “a  b”
s.isdigit()             # False
s[0:5]                  # “Hello” (slicing)

int("42")               # 42
float("3.14")           # 3.14
str(42)                 # "42"
bool(0)                 # False
bool("")                # False
bool("anything")        # True
list("abc")             # ['a', 'b', 'c']
tuple([1, 2, 3])        # (1, 2, 3)
set([1, 1, 2, 3])       # {1, 2, 3}

nums = [1, 2, 3, 4, 5]
mixed = [1, "two", 3.0, True]
nums[0]                 # 1 (first)
nums[-1]                # 5 (last)
nums[1:3]               # [2, 3] (slice)
nums[:3]                # [1, 2, 3]
nums[::2]               # [1, 3, 5] (every 2nd)
nums[::-1]              # [5, 4, 3, 2, 1] (reversed)
len(nums)               # 5

nums = [1, 2, 3]
nums.append(4)          # [1, 2, 3, 4]
nums.insert(0, 0)       # [0, 1, 2, 3, 4]
nums.extend([5, 6])     # [0, 1, 2, 3, 4, 5, 6]
nums.remove(0)          # removes first occurrence
nums.pop()              # removes & returns last
nums.pop(0)             # removes & returns index 0
nums.sort()             # sort in place
nums.sort(reverse=True) # descending
nums.reverse()          # reverse in place
nums.index(3)           # find index of value
nums.count(2)           # count occurrences
nums.copy()             # shallow copy

# Basic
squares = [x**2 for x in range(10)]
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
With condition
evens = [x for x in range(20) if x % 2 == 0]
Transform
names = [“alice”, “bob”]
upper = [n.upper() for n in names]
Nested
matrix = [[1,2],[3,4]]
flat = [x for row in matrix for x in row]  # [1,2,3,4]
With else
labels = [“even” if x%2==0 else “odd” for x in range(5)]

user = {"name": "Alice", "age": 30, "active": True}
user[“name”]                # “Alice”
user.get(“email”, “N/A”)    # “N/A” (default if missing)
user[“email”] = “a@b.com”   # add/update
del user[“active”]          # delete key
“name” in user              # True
len(user)                   # number of keys

d = {"a": 1, "b": 2}
d.keys()                # dict_keys([‘a’, ‘b’])
d.values()              # dict_values([1, 2])
d.items()               # dict_items([(‘a’, 1), (‘b’, 2)])
d.update({“c”: 3})      # merge another dict
d.pop(“a”)              # remove & return value
d.setdefault(“d”, 4)    # set if missing, return value
Dict comprehension
squares = {x: x**2 for x in range(5)}
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
Merge (Python 3.9+)
merged = {**d, **{“e”: 5}}
merged = d | {“e”: 5}   # Python 3.9+

if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teen")
else:
    print("Child")
Ternary
status = “adult” if age >= 18 else “minor”
Match statement (Python 3.10+)
match command:
case “quit”:
exit()
case “hello”:
print(“Hi!”)
case _:
print(“Unknown”)

# For loop
for i in range(5):          # 0, 1, 2, 3, 4
for i in range(2, 10, 2):   # 2, 4, 6, 8
for item in my_list:
for i, item in enumerate(my_list):  # with index
for key, val in my_dict.items():
While loop
while condition:
do_something()
Loop control
break       # exit loop
continue    # skip to next iteration
Else clause (runs if loop completes without break)
for item in items:
if item == target:
break
else:
print(“Not found”)

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"
greet(“Alice”)              # “Hello, Alice!”
greet(“Bob”, “Hi”)          # “Hi, Bob!”
*args and **kwargs
def func(*args, **kwargs):
print(args)     # tuple of positional args
print(kwargs)   # dict of keyword args
func(1, 2, name=“Alice”)
(1, 2)
{‘name’: ‘Alice’}
Lambda
square = lambda x: x**2
sorted(users, key=lambda u: u[“age”])

def timer(func):
    import time
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        print(f"{func.__name__} took {time.time()-start:.2f}s")
        return result
    return wrapper
@timer
def slow_function():
import time
time.sleep(1)
slow_function()  # “slow_function took 1.00s”

class User:
    def __init__(self, name, age):
        self.name = name
        self.age = age
def greet(self):
    return f"Hi, I'm {self.name}"

def __str__(self):
    return f"User({self.name}, {self.age})"

def __repr__(self):
    return f"User('{self.name}', {self.age})"
user = User(“Alice”, 30)
print(user.greet())     # “Hi, I’m Alice”

from dataclasses import dataclass
@dataclass
class User:
name: str
age: int
active: bool = True
user = User(“Alice”, 30)
Auto-generates init, repr, eq

# Read entire file
with open("file.txt", "r") as f:
    content = f.read()
Read lines
with open(“file.txt”) as f:
lines = f.readlines()       # list of lines
# or
for line in f:
print(line.strip())
Write
with open(“file.txt”, “w”) as f:
f.write(“Hello\n”)
Append
with open(“file.txt”, “a”) as f:
f.write(“More text\n”)
JSON
import json
with open(“data.json”) as f:
data = json.load(f)
with open(“data.json”, “w”) as f:
json.dump(data, f, indent=2)

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Can't divide by zero")
except (TypeError, ValueError) as e:
    print(f"Error: {e}")
except Exception as e:
    print(f"Unexpected: {e}")
else:
    print("No error occurred")
finally:
    print("Always runs")
Raise exceptions
raise ValueError(“Invalid input”)
Custom exceptions
class MyError(Exception):
pass

import os
from pathlib import Path
os.getcwd()                     # current directory
os.listdir(”.”)                 # list files
os.path.exists(“file.txt”)     # check if exists
os.makedirs(“dir/sub”, exist_ok=True)
os.environ.get(“API_KEY”, "")  # env variable
Pathlib (modern, preferred)
p = Path(“src/app.py”)
p.exists()                      # True/False
p.read_text()                   # read file
p.write_text(“content”)         # write file
p.parent                        # Path(‘src’)
p.stem                          # ‘app’
p.suffix                        # ‘.py’
list(Path(”.“).glob(”**/*.py”)) # find all .py files

from datetime import datetime, timedelta
now = datetime.now()
today = datetime.today().date()
ts = datetime.fromtimestamp(1710374400)
now.strftime(“%Y-%m-%d %H:%M”)     # “2026-03-14 10:30”
datetime.strptime(“2026-03-14”, “%Y-%m-%d”)
tomorrow = now + timedelta(days=1)
diff = datetime(2026, 12, 31) - now  # timedelta object

import re
re.search(r”\d+”, “age: 30”)       # match object
re.findall(r”\d+”, “1 and 2 and 3”) # [‘1’, ‘2’, ‘3’]
re.sub(r”\s+”, ” ”, “too   many”)   # “too many”
re.split(r”[,;]”, “a,b;c”)          # [‘a’, ‘b’, ‘c’]
match = re.search(r”(\w+)@(\w+)”, “user@host”)
match.group(1)                       # “user”
match.group(2)                       # “host”