Python: list comprehension, do f(x) if x exists?

Question

How can I do something like the following in Python?

row = [unicode(x.strip()) if x for x in row]

Basically, a list comprehension where you carry out a function if the variable exists.

Thanks!

You say, if the variable exists, but I think you mean, if it is not None. The "for x in row" bit will walk through all of the "variables" in row. — Aaron H., Nov 23 '10 at 19:21
I think this question very similar to http://stackoverflow.com/questions/4260280/python-if-else-in-list-comprehension should not re-post the same question twice — anijhaw, Nov 23 '10 at 21:58

score 19 · Accepted Answer · answered Nov 23 '10 at 19:19

19

The "if" goes at the end"

row = [unicode(x.strip()) for x in row if x]

answered Nov 23 '10 at 19:19

Adam Vandenberg

Perfect, thank you. As @delnan comments above, what I really need is 'x is not None' - though that's my fault for an ambiguous explanation. – AP257 Nov 23 '10 at 19:37

score 3 · Answer 2 · answered Nov 23 '10 at 19:19

3

So close.

row = [unicode(x.strip()) for x in row if x]

answered Nov 23 '10 at 19:19

score 3 · Answer 3 · answered Nov 23 '10 at 19:20

3

Not sure about the goals, but this should work

row = [unicode(x.strip()) for x in row if x ]

answered Nov 23 '10 at 19:20

pyfunc

score 1 · Answer 4 · answered Nov 21 '11 at 00:25

1

Maybe you're were thinking of the ternary operator syntax as used if you want if/else, e.g.:

row = [unicode(x.strip()) if x is not None else '' for x in row ]

or whatever you'd want to do.

answered Nov 21 '11 at 00:25

Morten Jensen

4 Answers4