[Tutor] I'm puzzled

[Vincent Zee]

On Sunday, 22 January 2006 at 16:07:06 -0800, bob wrote:
> At 03:46 PM 1/22/2006, Vincent Zee wrote:
> >Why will this little program crash when you enter the enter key?
> 
> Thank you for including the "traceback" message in your 2nd post.
> 
> Index error means you tried to reference an element of a sequence 
> that is not there. a is the empty string when you just hit enter to 
> the raw_input request. It therefore has no elements, so a[0] raises 
> the exception.
> 
> To avoid this test first for len(a) > 0.
> 
> >while True:
> >    a = raw_input('number? ')
> >    if a.isdigit():
> >        print 'isdigit'
> >    elif a[0] == '-' and a[1:].isdigit():
> >        print '- + isdigit'
> >    elif a == 'q':
> >        break
> >    else:
> >        print 'no digit'
> 

Ah, thank you Bob for the explanation.
I understand now.

/\
Vincent