Looping through collections

Lists

Each:

for item in collection:
    process(item)

Back to front:

for item in reversed(collection):
    process(item)

With index

for index, item in enumerate(collection):
    process(index, item)

Map (returns map object — ‘listify’ with list(mapObject)):

map(lambda x: x * 2, numbers)

def process(number):
    return number * 2

map(process, numbers)

Using list comprehensions as a kind of a map().

[x * 2 for x in [1, 2, 3, 4]]

Sets

Each key:

for key in {'height', 'weight'}:
    process(key)

Dicts

Each key:

for key in {'height': 100, 'width': 200}:
    process(key)

Each value:

for value in {'height': 100, 'width': 200}.values():
    process(value)

Each key/value:

for key, value in {'height': 100, 'width': 200}.items():
    process(key, value)

Strings

Each char:

for char in 'string':
     process(char)