Comprehensions & Generators — Pythonic Power

List comprehension:

# Instead of:
squares = []
for x in range(10):
    squares.append(x**2)

# Write:
squares = [x**2 for x in range(10)]

# With condition:
evens = [x for x in range(20) if x % 2 == 0]

Dict comprehension:

word_lengths = {word: len(word) for word in ["cat", "elephant", "dog"]}
# {"cat": 3, "elephant": 8, "dog": 3}

Set comprehension:

unique_lengths = {len(word) for word in ["cat", "dog", "elephant"]}
# {3, 8}

Generators — memory-efficient iteration:

# List: loads ALL values into memory
big_list = [x**2 for x in range(1000000)]

# Generator: produces values one at a time
big_gen = (x**2 for x in range(1000000))

# Generator function:
def countdown(n):
    while n > 0:
        yield n
        n -= 1

Reference:

Wikipedia: List Comprehension

https://en.wikipedia.org/wiki/List_comprehension