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Possible Duplicate:
How do I check if a string is a number in Python?
Python - Parse String to Float or Int

For example, I want to check a string and if it is not convertible to integer(with int()), how can I detect that?

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Figen Güngör
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  • There is already a solution here http://stackoverflow.com/questions/354038/how-do-i-check-if-a-string-is-a-number-in-python – ronak Sep 17 '12 at 19:44
  • For clarity, should '-99' be allowed? What about '+123'? Or " 1729 " (integer with leading and trailing spaces). '0x123'? – Mark Dickinson Sep 17 '12 at 19:52
  • @MarkDickinson -- why wouldn't `'-99'` be allowed? – mgilson Sep 17 '12 at 19:57
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    @mgilson: No idea---I can't guess what the OP's usecase is. But it's an obvious example that isn't served so well by the 'isdigit' answer. – Mark Dickinson Sep 17 '12 at 19:59

2 Answers2

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Use the .isdigit() method:

>>> '123'.isdigit()
True
>>> '1a23'.isdigit()
False

Quoting the documentation:

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

For unicode strings or Python 3 strings, you'll need to use a more precise definition and use the unicode.isdecimal() / str.isdecimal() instead; not all Unicode digits are interpretable as decimal numbers. U+00B2 SUPERSCRIPT 2 is a digit, but not a decimal, for example.

Martijn Pieters
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33

You can always try it:

try:
   a = int(yourstring)
except ValueError:
   print "can't convert"

Note that this method outshines isdigit if you want to know if you can convert a string to a floating point number using float

mgilson
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