Question

When I do

dict = {'Alice': '7898', 'Beth': '9102', 'Cecil': '3258'}
print filter(lambda x: x, dict['Alice'])

it shows: 7898

When I do the next

dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}
print filter(lambda x: x=="2341", dict['Alice'])

it shows:

Why it doesn’t show True. How to get True ?

Answer 1

It looks like your misunderstanding is with filter, to me. You pass a predicate function and an iterable object to filter. It creates a new object containing those items from the first iterable for which the predicate returns a true value (not necessarily True itself, just something that tests as true). The iterable in the two cases is the string '2341', which means the individual letters are tested. Of course the string '2341' is not equal to any of '2', ‘3', '4', or '1'.

Try it with a tuple and it’s easier to see what’s going on:

>>> tup = tuple(dict['Alice'])
>>> tup
('7', '8', '9', '8')
>>> filter(lambda x: x, tup)
('7', '8', '9', '8')
>>> tup
('7', '8', '9', '8')
>>> filter(lambda x: x, tup)
('7', '8', '9', '8')
>>> filter(lambda x: x=="2341", tup)
()