[Tutor] n.isalnum() is failing

[bhaaluu]

Greetings,

Perhaps the first thing you should do, before checking
whether the user entered 'aaaa' instead of '2000' is to
get the leap year function working properly.

Definition:
Leap years occur according to the following formula:
       a leap year is divisible by four,
       but not by one hundred,
       unless it is divisible by four hundred.

I find that definition to be a wee bit misleading.
This might help:

A leap year is divisible by four, with a REMAINDER of zero.
The remainder of a division is found in python with the "%" operator.
So you might want to check and see IF the remainders are zero or one,
TRUE or FALSE.

When I run your program, entering two four-digit years,
this is the output:

This program finds all leap years between two dates.

Enter yyyy for beginning year : 1995
Enter yyyy for ending year : 2000

1995 -- leap year!
1996 -- leap year!
1997 -- leap year!
1998 -- leap year!
1999 -- leap year!
2000 -- leap year!
Done!

Since we know that ALL of those years can't be leap years,
it means that your leap() function isn't doing something right?
I suggest that you get leap() working properly first, then tackle
the other problem.

Cheers!
-- 
bhaaluu at gmail dot com

On 7/3/07, Terry <terry.kemmerer at gmail.com> 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
>
>