Python Comprehensions

# Basic list comprehension
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]
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# String operations
words = ['hello', 'world', 'python']
upper = [w.upper() for w in words]
# ['HELLO', 'WORLD', 'PYTHON']

# If-else in comprehension
result = [x if x % 2 == 0 else -x for x in range(5)]
# [0, -1, 2, -3, 4]

# Nested comprehension
matrix = [[i*j for j in range(3)] for i in range(3)]
# [[0,0,0], [0,1,2], [0,2,4]]

# Flatten nested list
nested = [[1,2], [3,4], [5,6]]
flat = [x for sublist in nested for x in sublist]
# [1, 2, 3, 4, 5, 6]

# Basic dict comprehension
squares = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# From two lists
keys = ['a', 'b', 'c']
values = [1, 2, 3]
d = {k: v for k, v in zip(keys, values)}
# {'a': 1, 'b': 2, 'c': 3}

# Swap keys and values
original = {'a': 1, 'b': 2}
swapped = {v: k for k, v in original.items()}
# {1: 'a', 2: 'b'}

# Basic set comprehension
squares = {x**2 for x in range(10)}
# {0, 1, 4, 9, 16, 25, 36, 49, 64, 81}

# Remove duplicates
numbers = [1, 2, 2, 3, 3, 3, 4]
unique = {x for x in numbers}
# {1, 2, 3, 4}

# With condition
text = 'Hello World'
vowels = {c.lower() for c in text if c.lower() in 'aeiou'}
# {'e', 'o'}