reducing if statements and error handling
aleax at aleax.it
Tue Aug 21 18:16:44 CEST 2001
"Jeff" <jhardcastle at solarc.com> wrote in message
news:e33814e8.0108210508.7644eeb5 at posting.google.com...
> 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
That's what string-method isdigit is for, indeed:-).
> def checkvalue(value):
> if value.isdigit():
> print 'success: ' + value + ' is a valid entry'
> return 1
> print 'error: ' + value + ' is NOT a valid entry'
> return -1
> 1) can I reduce this "if" logic down to one statement, perhaps using
No, there is no way you can both print and return in "one statement"
(except a compound statement, like the if/else you're using here).
With some *HORRIDLY* convoluted obfuscations you might be able to
substitute the print statements with sys.stdout.write(...) calls,
and squeeze the whole body of function checkvalue into a single
return statement which emits messages as a "side effect"...
but why ever would you want to compose such a monstruosity...?
E.g., something like:
'error: %s is NOT a valid entry'
'success: %s is a valid entry',][value.isdigit()])%value)
and 0) or [-1,1][value.isdigit()]
...but why would anybody obfuscate in such fashion...?
Besides, that wouldn't work if you wanted to raise in certain
cases only, anyway -- raise is also a statement. And (see
below) it's better to raise on invalid value here...
> 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
Of course! E.g.:
> 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?
Far better to raise here: this way, you can design upper layers
to let the exception propagate up to whatever level can best
handle it -- if you use return, you rely on the specific level
that's calling this function to check for the error-return value.
Not a good idea if you can avoid it, and raise lets you avoid it.
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