Python的`filter`函数_python self.filter

python的这个内置函数我之前竟然没用过hhh
看下文档就懂了:

Init signature: filter(self, /, *args, **kwargs)
Docstring:     
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.
Type:           type
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返回一个迭代器，
如果第一个参数为function，而不为None，则新迭代器为:

def new_iter():
	for item in 旧迭代器:
		if function(item):
			yield item
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如果function为None，则返回为true的项目:

def new_iter():
	for item in 旧迭代器:
		if bool(item):
			yield item
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