python内置函数之filter()

先看官方解释

"""
    filter(function or None, iterable) --> filter object
    
    Return an iterator yielding those items of iterable for which function(item)
    is true. If function is None, return the items that are true.
"""

它的用法有两点：

• function做为过滤条件，过滤出iterable中满足条件的元素，以迭代器的形式返回
• 如果function为None，则返回iterable为true的元素，以迭代器的形式返回

注意：python2返回的结果存放在列表中，python3返回迭代器对象

用法举例1

# 过滤出列表中大于0的元素
g = filter(lambda x: x > 0, [1, 0, 3, -3, 12])
for i in g:
    print(i, end=',')
    
# output: 1,3,12,

用法举例2

# 过滤出列表中的奇数
g = filter(lambda x: x %2 == 1, [1, 0, 3, -3, 12])
for i in g:
    print(i, end=',')

# output: 1,3,-3,

用法举例3

# 过滤出不为假的元素
g = filter(None, ['abc', 0, False, 'abcde', 'abcdefg'])
for i in g:
    print(i, end=',')

# output: abc,abcde,abcdefg,

g = filter(None, [])
for i in g:
    print(i, end=',')
# output: 返回空