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Question

How to check if an element of a list is a number?

Answer 1

+9 A:

try:
  i = int(temp[0])
except ValueError:
  print "not an integer\n"

try:
  i = float(temp[0])
except ValueError:
  print "not a number\n"

If it must be done with a regex:

import re
re.match( '^[-+]?(([0-9]+([.][0-9]*)?)|(([0-9]*[.])?[0-9]+))$', temp[0] )

eruciform 2010-07-12 01:09:50

If you're going to check for any other things inside the try block, make sure you `except ValueError`

Justin Poliey 2010-07-12 01:13:34

How does this have the most votes? Empty except's, seriously? Edit: Oh, he fixed it now .. still, why can't you use regex as he asked, or one of the built-in functions? This is a code-heavy way

Bartek 2010-07-12 01:14:53

I'm all for telling him the right thing to do, but you explicitly ignored the part of the question that said "use a regular expression" :)

Stephen 2010-07-12 01:14:54

@justin: thanks, updated. @stephen: he said "some sort of regex" - I think he just wants a solution...

eruciform 2010-07-12 01:16:17

You're probably right. Answers that don't use regex on questions that ask for regex always seem to get a lot of votes :)

Stephen 2010-07-12 01:30:22

http://regex.info/blog/2006-09-15/247

Johnsyweb 2010-07-12 11:12:26

updated: added regex solution as well

eruciform 2010-07-12 12:48:49

That regex would accept things like "", ".", "-.", "0." which aren't traditionally accepted as numerics (well, "0." is in Python). So, +1 for the non-regex solution, will be faster, too.

Korbinian 2010-07-12 20:27:43

@korbinian: true. updated. :-)

eruciform 2010-07-12 21:05:20

Answer 2

+1 A:

Using regular expressions (because you asked):

>>> import re
>>> if re.match('\d+', temp[0]): print "it's a number!"

Otherwise, just try to parse as an int and catch the exception:

>>> int(temp[0])

Of course, this all gets (slightly) more complicated if you want floats, negatives, scientific notation, etc. I'll leave that as an exercise to the asker :)

Stephen 2010-07-12 01:10:01

Thanks a lot for your help guys.

DGT 2010-07-12 01:20:22

Answer 3

+2 A:

If you are just expecting a simple positive number, you can use the isDigit method of Strings.

if temp[0].isdigit(): print "It's a number"

linead 2010-07-12 01:11:47

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