Newbie Help

Peter Hansen peter at engcorp.com
Mon Jun 21 08:12:17 CEST 2004


cronje_med wrote:

> Ok, so I'm a bit new at this, so please don't make fun of me too much.

You won't find folks doing that around here... this is a nice
newbie-friendly group, for the most part (even if some misinterpret
my attempts at humour :-).

> I was trying to make a math function that wouldn't pull a NameError 
> if I didn't enter a number or variable containing a number. Here's 
> what I have:
> 
> def math(num):
>         if num.isdigit() == 1:
>             print "Is a number!"
>             return num
>         else:
>             print "Is not a number!"
>             return num
> 
> 
>>>>math(5+5)
> AttributeError: 'int' object has no attribute 'isdigit'
> 
>>>>math("5+5")
> Is not a number!
> '5+5'
> 
>>>>math("5+x")
> Is not a number!
> '5+x'

def testNum(num):
     try:
         num + 1
         print 'Is a number!'
         return num
     except TypeError:
         print 'Is not a number!'
         return num

In Python, the most elegant way to check something like that is
to try to use it _as_ such a thing.  If that fails, catch the
exception that's raised and carry on...  The above tries to
add one to the number, which should work for anything that
acts like a number, but fail for most other things...

-Peter



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