Idiomatic Python

Idiomatic Python gists.

• Loop a list with index:

for index, value in enumerate([1, 2, 3, 4, 5]):
    print("%s -> %s" % (index, value))

• Loop a dictionary's key-value pairs:

for key, value in {1: 'one', 2: 'two', 3: 'three'}.items():
    print("%s -> %s" % (key, value))

• Loop backward a list:

for value in reversed([1, 2, 3, 4, 5]):
    print(value)

• Loop backward a list with index:

for index, value in reversed([i for i in enumerate([1, 2, 3, 4, 5])]):
    print("%s -> %s" % (index, value))

• Default dictionary - Group items with same value:

from collections import defaultdict

# group items with same value
groups = defaultdict(list)

for value in [1,1,2,2,3,3]:
    groups[value].append(n)