[Tutor] n.isalnum() is failing

[Wolfram Kraus]

Use isdigit instead of isalnum.

HTH,
Wolfram

On 03.07.2007 09:51, Terry wrote:
> Hi!
> 
> I am running Python 2.5, and I have an IF statement in the below program
> that does not seem
> to be doing it's job. The program simply acquires a range of years from
> the user and prints out
> all the leap years between the two dates. I am having trouble in
> trapping for possible user
> errors. I am using x.isalnum() to check that I have a number for each
> year entered, and it
> doesn't look to me like it is functioning properly.
> 
> When I purposely enter bad data, such as 'aaaa' for one of the a year
> entries, the IF statement:
> 
>         if start.isalnum() == 1 and end.isalnum() == 1:
> 
> -Fails to detect that 'aaaa' is not a number and lets the program then
> die tragically a horrible
> sudden awkward death on the very next line:
> 
>         start = int(start); end = int(end)
> 
> Traceback (most recent call last):
>   File "/home/lucky/Documents/Python_Programs/leap_years.py", line 119,
> in <module>
>     start = int(start); end = int(end)
> ValueError: invalid literal for int() with base 10: 'aaaa'
> 
> If I say on the commandline:
> 
>>>> n = 'aaaa'
>>>> n.isalnum()
> True                     <------------It seems to me it should be saying
> False!!!
>>>>
> 
> 
> My program starts here:
> 
> def leap(yyyy):
>     answer = 0
>     t1 = yyyy / 4
>     if t1 == int(t1):
>         t2 = yyyy / 100
>         t3 = yyyy / 400
>         if t2 <> int(t2) or t3 == int(t3):
>             answer = "-- leap year!"
>     return answer
> 
> print "This program finds all leap years between two dates.";print;print
> 
> start = raw_input("Enter yyyy for beginning year : ")
> end = raw_input("Enter yyyy for ending year : ")
> 
> if len(start) == 4 and len(end) == 4:
>     if start.isalnum() == 1 and end.isalnum() == 1:                  
> #<----------fails to detect 'aaaa' as not a number
>         start = int(start); end =
> int(end)                                       #<----------commits
> suicide here
>         if start > 0 and end > start:
>             print; print
>             for i in range(start, end + 1):
>                 answer = leap(i)
>                 if answer != 0:
>                     print i, answer
> print "Done!"
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> http://mail.python.org/mailman/listinfo/tutor