Pythonic way to determine if a string is a number

[Python Nutter]

silly me, forgot to mention

build a set from digits + '.' and use that for testing.

Cheers,
PN


2009/2/16 Python Nutter <pythonnutter at gmail.com>:
> Type casting seems to be the wrong way to go about this.
>
> teststring = '15719'
> teststring.isdigit()
> returns True
>
> That takes care of integers.
>
> from string import digits
> digits
> '0123456789'
>
> now you have all the digits and you can do set testing in your logic
> to see if the teststring has anything in digits
>
> A dumb way to test is alphanumeric
>
> teststring2 = '105.22'
> teststring2.isalnum()
> returns True
>
> now you can go on from there and test to further to eliminate
> 'abcd385laf8' which on alnum() also returns true.
>
> Have fun,
> Cheers,
> PN
>
>
> 2009/2/16  <python at bdurham.com>:
>> What's the Pythonic way to determine if a string is a number? By
>> number I mean a valid integer or float.
>>
>> I searched the string and cMath libraries for a similar function
>> without success. I can think of at least 3 or 4 ways to build my
>> own function.
>>
>> Here's what I came up with as a proof-of-concept. Are there
>> 'better' ways to perform this type of test?
>>
>> Thanks,
>> Malcolm
>>
>> <code>
>> def isnumber( input ):
>>    try:
>>        if '.' in input:
>>            num = float( input )
>>        else:
>>            num = int( input )
>>        return True
>>
>>    except ValueError:
>>        return False
>>
>> if __name__ == '__main__':
>>    tests = """
>>        12
>>        -12
>>        -12.34
>>        .0
>>        .
>>        1 2 3
>>        1 . 2
>>        just text
>>    """
>>
>>    for test in tests.split( '\n' ):
>>        print 'test (%0s), isnumber: %1s' % \
>>          ( test.strip(), isnumber( test ) )
>>
>> </code>
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>