Detailed explanation of the usage of filter in Python

Detailed explanation of the usage of filter in Python

1 class filter(object)
2  |  filter(function or None, iterable) --> filter object
3  |  
4  |  Return an iterator yielding those items of iterable for which function(item)
5  |  is true. If function is None, return the items that are true.

filter reads in all items of iterable, determines whether these items are true for function, and returns a list containing all items that are true Iterator of items. If function is None, returns a non-empty item.

1 In [2]: import re
2 In [3]: i = re.split(',',"123,,123213,,,123213,")
3 In [4]: i4 Out[4]: ['123', '', '123213', '', '', '123213', '']

At this time, list i contains an empty string.

1 In [7]: print(*filter(None, i))
2 123 123213 123213

At this time, the filter filters out the empty strings in the list and obtains an iterator containing only non-empty strings.

In [9]: print(list(filter(lambda x:x=='', i)))
['', '', '', '']

Since lambda is true for empty strings, filter filters out non-empty strings, leaving only empty strings.

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