[Tutor] check_range

Brian van den Broek bvande at po-box.mcgill.ca
Wed Dec 15 01:39:06 CET 2004

Marc Gartler said unto the world upon 2004-12-14 18:12:
> Hi all,
> I am fairly new to both Python & programming, and am attempting to 
> create a function that will test whether some user input is an integer 
> between 10 and 89, but the check isn't happening...
> def check_range(myrange):
>     if range(myrange) != range(10,89):
>         return "False"
>     else:
>         return "True"
> ...this gets called later via:
>         if check_range(input):
>             done = "True"
>                 return int(input)
> What am I doing wrong?
> Thanks!

Hi Marc,

Welcome to Python and the list. :-)

Others have pointed out how to solve your immediate problem with in or a 
comparison, and that you can just return True and False unquoted. (They 
are special builtin objects, so making strings for them isn't needed.)

A minor correction to Kent's suggestion, though. He suggested to use
10 < x < 90, but since I gather you want 10 to return True, you need
9 < x < 90:

 >>> 10 < 10 < 90
 >>> 9 < 10 < 90

This sort of thing is an "off by 1 error" and will happen to you all the 
time :-(

I have a some style suggestions for you, too.

Try it this way:

 >>> def check_in_range(value):
         in_range = False
         if 9 < value < 90:
             in_range = True
         return in_range

 >>> check_in_range(35)

This way, by setting a name to point to False, and over-riding that when 
the test is met, there is only a single return statement. That is often 
considered a good thing. This function is too small for it to matter 
lots, but have multiple returns can make the debugging a bit harder.

Another tip is that for debugging such things it often helps to use 
print statements when things don't go as expected. If you'd added them 
to your original function like so:

 >>> def check_range(myrange):
	print range(myrange)
	print range(2,5)
	if range(myrange) != range(2,5):
		return "False"
	        return "True"
 >>> check_range(3)
[0, 1, 2]
[2, 3, 4]

The problem would have likely been much more clear.


Brian vdB

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