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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Karl Knechtel
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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
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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
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@MarkDickinson -- why wouldn't `'-99'` be allowed? – mgilson Sep 17 '12 at 19:57
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1@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
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See also: https://stackoverflow.com/questions/379906/python-parse-string-to-float-or-int – Karl Knechtel Jul 21 '22 at 23:21
2 Answers
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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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5I didn't downvote, but `" 1234".isdigit()` will return `False` even though `int` will happily ignore the space in the front. – mgilson Sep 17 '12 at 19:49
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2@user1655481: that's not a number either, it's a python hex literal. `int('0x12')` throws ValueError unless you specify a base. – Martijn Pieters Sep 17 '12 at 19:51
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@mgilson: that's kind of the point of the function. It depends on your usecases as to what you need, if `.strip()` is needed, etc. – Martijn Pieters Sep 17 '12 at 19:52
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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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