Python: 内包表記のチートシート

リスト内の全ての要素を２倍にする

mylist = [1, 2, 3, 4, 5, 6, 7, 8, 9]
newlist = [n*2 for n in mylist]
print(newlist)

[2, 4, 6, 8, 10, 12, 14, 16, 18]

リスト内の偶数のみ取り出す

mylist = [1, 2, 3, 4, 5, 6, 7, 8, 9]
newlist = [n for n in mylist if n%2==0]
print(newlist)

[2, 4, 6, 8]

リスト内の偶数は”even”、奇数は”odd”とする

mylist = [1, 2, 3, 4, 5, 6, 7, 8, 9]
newlist = ["even" if n%2==0 else "odd" for n in mylist]
print(newlist)

['odd', 'even', 'odd', 'even', 'odd', 'even', 'odd', 'even', 'odd']

辞書の要素を全て２倍にする

mydict = {"a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
newdict = {k:v*2 for k,v in mydict.items()}
print(newdict)

{'a': 2, 'c': 6, 'b': 4, 'e': 10, 'd': 8}

辞書の要素が偶数であるもののみ取り出す

mylist = [1, 2, 3, 4, 5, 6, 7, 8, 9]
newdict = {k:v for k,v in mydict.items() if v%2==0 }
print(newdict)

{'b': 2, 'd': 4}