[Tutor] n.isalnum() is failing
bhaaluu
bhaaluu at gmail.com
Tue Jul 3 11:06:20 CEST 2007
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!"
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