lists
List comprehension patterns
Pythonic ways to create and transform lists.
# Basic comprehension
squares = [x**2 for x in range(10)]
# With condition
evens = [x for x in range(20) if x % 2 == 0]
# Nested comprehension (flatten)
flat = [x for row in matrix for x in row]
# Dict comprehension
word_lengths = {w: len(w) for w in words}
# Set comprehension
unique_lengths = {len(w) for w in words}dictionaries
Merge dictionaries
Multiple ways to merge dicts in Python.
# Python 3.9+ (cleanest)
merged = dict_a | dict_b
# Update in place
dict_a |= dict_b
# Python 3.5+ (spread)
merged = {**dict_a, **dict_b}
# Older Python
merged = dict_a.copy()
merged.update(dict_b)files
Read and write files
Common file operations with context managers.
# Read entire file
with open('file.txt', 'r') as f:
content = f.read()
# Read lines
with open('file.txt') as f:
lines = f.readlines()
# Write file
with open('output.txt', 'w') as f:
f.write('Hello, world!')
# Read JSON
import json
with open('data.json') as f:
data = json.load(f)
# Write JSON
with open('output.json', 'w') as f:
json.dump(data, f, indent=2)strings
String formatting
Modern f-strings and formatting techniques.
name, age = "Alice", 30
# f-string (recommended)
msg = f"Hello, {name}! You are {age}."
# f-string with expressions
msg = f"Next year: {age + 1}"
msg = f"Upper: {name.upper()}"
# Number formatting
f"{1234567:,}" # '1,234,567'
f"{3.14159:.2f}" # '3.14'
f"{0.856:.1%}" # '85.6%'
f"{42:08b}" # '00101010' (binary)
# Padding
f"{'hi':>10}" # ' hi' (right-align)
f"{'hi':<10}" # 'hi ' (left-align)
f"{'hi':^10}" # ' hi ' (center)