reducing if statements and error handling

[Doug Fort]

Jeff wrote:

> Another easy newbie question here...  Suppose I have a method that
> accepts a string (called 'value') as an argument.  I want the method
> to check to see if the contents of the string is all numbers.  Here's
> my logic:
> 
> def checkvalue(value):
>    if value.isdigit():
>         print 'success: ' + value + ' is a valid entry'
>         return 1
>    else:
>         print 'error: ' + value + ' is NOT a valid entry'
>         return -1
> 
> Questions:
> 1) can I reduce this "if" logic down to one statement, perhaps using
> lambdas?
> 2) is there a recommended approach for throwing errors?  In this case,
> I'd want to throw an error if the text is not a number and stop
> processing.  Can I define a custom exception to do that?  Should I
> catch the error in the logic that called the method and throw the
> exception there if the method returns a "-1", or should I throw the
> exception here?
>               
> Thanks!
> Jeff
> 

Instead of the whole checkvalue function, why not say

try:
    number = int(value)
except ValueError, instance:
    print instance

With regards to number 2), I find that when I use exceptions judiciously I 
don't need to have functions return a 'success' value. You can define 
custom exceptions easily. It's a good idea to derive them from Exception, 
but not absolutely neccessary.
-- 
Doug Fort <dougfort at dougfort.net>
http://www.dougfort.net

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