python的 filter, map, reduce, lambda, list comprehension

>>> foo = [2, 18, 9, 22, 17, 24, 8, 12, 27]
>>>
>>> print(filter(lambda x: x % 3 == 0, foo))
[18, 9, 24, 12, 27]
>>>
>>> print(map(lambda x: x * 2 + 10, foo))
[14, 46, 28, 54, 44, 58, 26, 34, 64]
>>>
>>> print(reduce(lambda x, y: x + y, foo))
139

上面的map和filter都可以用列表推导改写

print(filter(lambda x: x % 3 == 0, foo))
等价于
print([x for x in foo if x % 3 == 0])

print(map(lambda x: x * 2 + 10, foo))
等价于
print([x * 2 + 10 for x in foo])

求2到49范围内的素数

>>> nums = range(2, 50)
>>> for i in range(2, 8):
nums = [x for x in nums if x==i or x % i != 0]
>>> nums
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]