Python: Test if value can be converted to an int in a list comprehension

Question

Basically I want to do this;

return [ row for row in listOfLists if row[x] is int ]

But row[x] is a text value that may or may not be convertible to an int

I’m aware that this could be done by:

try:
    int(row[x])
except:
    meh

But it’d be nice to do it is a one-liner.

Any ideas?

Asked By: Bolster

||

Answer 1

If you only deal with integers, you can use str.isdigit():

Return true if all characters in the string are digits and there is at least one character, false otherwise.

[row for row in listOfLists if row[x].isdigit()]

Or if negative integers are possible (but should be allowed):

row[x].lstrip('-').isdigit()

And of course this all works only if there are no leading or trailing whitespace characters (which could be stripped as well).

Answered By: Felix Kling

Answer 2

What about using a regular expression? (use re.compile if needed):

import re
...
return [row for row in listOfLists if re.match("-?d+$", row[x])]

Answered By: tokland

Answer 3

Or

return filter(lambda y: y[x].isdigit(), listOfLists)

or if you need to accept negative integers

return filter(lambda y: y[x].lstrip('-').isdigit(), listOfLists)

As fun as list comprehension is, I find it less clear in this case.

Answered By: CoatedMoose

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