filter( function, list)
Construct a list from those elements of list for which function returns true. list may be either a sequence, a container which supports iteration, or an iterator, If list is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of list that are false (zero or empty) are removed.
Note that filter(function, list) is equivalent to [item for item in list if function(item)] if function is not None and [item for item in list if item] if function is None.
>>> l=[1,2,4,5,6,7,8,433,5,6,6,76,4,23,234,3,4,5,6]
>>> filter(lambda x:x<10 and x or 0,l)
[1, 2, 4, 5, 6, 7, 8, 5, 6, 6, 4, 3, 4, 5, 6]
>>> filter(l)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: filter expected 2 arguments, got 1
>>> filter(None,l)
[1, 2, 4, 5, 6, 7, 8, 433, 5, 6, 6, 76, 4, 23, 234, 3, 4, 5, 6]
>>> l
[1, 2, 4, 5, 6, 7, 8, 433, 5, 6, 6, 76, 4, 23, 234, 3, 4, 5, 6]
>>> ll=[3,0,5,7,5,3,0,5,9,6,0,3]
>>> filter(None,ll)
[3, 5, 7, 5, 3, 5, 9, 6, 3]
>>> help(filter)
Help on built-in function filter in module __builtin__:
filter(...)
filter(function or None, sequence) -> list, tuple, or string
Return those items of sequence for which function(item) is true. If
function is None, return the items that are true. If sequence is a tuple
or string, return the same type, else return a list.
>>>