How can I check if a string represents an int, without using try/except?

python string integer
Adam Matan picture Adam Matan · Aug 12, 2009 · Viewed 617.4k times · Source

Is there any way to tell whether a string represents an integer (e.g., '3', '-17' but not '3.14' or 'asfasfas') Without using a try/except mechanism?

is_int('3.14') = False
is_int('-7')   = True

Answer

SilentGhost picture SilentGhost · Aug 12, 2009

with positive integers you could use .isdigit:

>>> '16'.isdigit()
True

it doesn't work with negative integers though. suppose you could try the following:

>>> s = '-17'
>>> s.startswith('-') and s[1:].isdigit()
True

it won't work with '16.0' format, which is similar to int casting in this sense.

edit:

def check_int(s):
    if s[0] in ('-', '+'):
        return s[1:].isdigit()
    return s.isdigit()

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