[Tutor] Problem with a variable in a CGI program

[Mark Kels]

On Fri, 7 Jan 2005 11:16:29 -0800 (PST), Danny Yoo
<dyoo at hkn.eecs.berkeley.edu> wrote:
> 
> 
> On Fri, 7 Jan 2005, Mark Kels wrote:
> 
> > I started to read the following code (I will start working on it when
> > this problem is fixed) and it looks OK while I read it. But for some
> > reason it doesn't work...
> 
> Hi Mark,
> 
> Ok, let's take a look at the error message:
> 
> 
> > Traceback (most recent call last):
> >   File "C:\maillist.py", line 80, in ?
> >     useMailList.writelines(memMailList)     # Copy internal mailing list to file
> >
> > NameError: name 'memMailList' is not defined
> 
> Ok, good, so we know what we should look for: we should see where
> 'memMailList' is defined, and see if there's any way that the program flow
> can route around the definition.
> 
> Ok, I see it, embedded within the context of a try/except block.
> 
> ######
> try:
> 
>     ## some code before definition of memMailList...
> 
>     memMailList=useMailList.readlines()
> 
>     ## some more code cut...
> 
> finally:
>    useMailList=open("maillist.txt", "w")
>    useMailList.writelines(memMailList)
>    useMailList.close
>    print useFoot.read()
>    useHead.close;
>    useFoot.close;
> ######
> 
> There's one possibility that strikes me: it's very possible that in the
> code before the definition of memMailList might raise an exception, or
> exit out prematurely due to a sys.exit().  If that happens, then Python
> will finish things up by jumping into the 'finally' block.  And if that
> happens, then we haven't reached memMailList's definition, and the
> NameError is inevitable.
> 
> Here's a simplified example of what might be happening:
> 
> ###
> >>> try:
> ...     a = 42
> ...     5 / 0
> ...     b = 17
> ... finally:
> ...     print "a is", a
> ...     print "b is", b
> ...
> a is 42
> b is
> Traceback (most recent call last):
>   File "<stdin>", line 7, in ?
> NameError: name 'b' is not defined
> ###
> 
> A direct way to debug this is to drop the 'finally' block altogether.  If
> we do so, like this:
> 
> ######
> ## some code before definition of memMailList...
> 
> memMailList=useMailList.readlines()
> 
> ## some more code cut...
> 
> useMailList=open("maillist.txt", "w")
> useMailList.writelines(memMailList)
> useMailList.close
> print useFoot.read()
> useHead.close;
> useFoot.close;
> ######
> 
> then the real cause of the problem should pop up quickly.
> 
> A few more comments:
> 
> 1.  The calls to close() need parentheses.  Unlike some other programming
> languages, function calls fire off only with parens.  Instead of:
> 
>     useFoot.close
> 
> you probably want:
> 
>     useFoot.close()
> 
> 2.  I also see that the code is hardcoded to use Python 1.5.  Is there any
> way you can use a more modern version of Python?  The reason I ask is that
> recent versions of Python have really good modules for debugging CGI
> programs, including the excellent 'cgitb' module:
> 
>     http://www.python.org/doc/current/lib/module-cgitb.html
> 
> Writing CGI programs without 'cgitb' is almost criminal.  *grin*  If you
> can, use it.
> 
> 3.  The program is long.  Can you break it down into some functions?  The
> program looks like one big monolith, and I'm actually quite terrified of
> it.  *grin*
> 
> Small functions are much easier to debug, and more approachable for
> maintainers of the code.  This is a style critique, but it does matter
> because although computers don't care what code looks like, human
> programmers do.
> 
> 4.  Related to Comment Three is: there are way too many comments on the
> side margin.  Comments like:
> 
> ###
> if email != email2:                      # Checks to see if two entered
>                                          # email addresses match
>     print "Email addresses do not match" # If no match print error
>     sys.exit(0)                          # Exit script with error 0
> elif password != password2:              # Checks to see if two
>                                          # entered passwords match
>     print "Passwords do not match"       # If no match print error
>     sys.exit(0)                          # Exit script with error 0
> ###
> 
> are redundant, since they basically parrot what the code is doing.
> 
> Concise comments that explain the reason why the code is doing what it's
> doing can be more useful.  Comments are meant to show us authorial
> intension: if we were interested in what the code was actually doing, we'd
> just read the code.  *grin*
> 
> Something like:
> 
> ######
> 
> ## Check for valididated emails and passwords, and exit if either are
> ## invalid.
> if email != email2:
>     print "Email addresses do not match"
>     sys.exit(0)
> elif password != password2:
>     print "Passwords do not match"
>     sys.exit(0)
> ######
> 
> is probably sufficient.
> 
> Even better would be to break this out as a function:
> 
> ###
> def validateEmailsAndPasswords(email, email2, password, password2):
>     """Check for valididated emails and passwords, and exit if either are
>        invalid."""
>     if email != email2:
>         print "Email addresses do not match"
>         sys.exit(0)
>     elif password != password2:
>         print "Passwords do not match"
>         sys.exit(0)
> ###
> 
> but I guess we should take this one step at a time.
> 
> If you have any questions, please feel free to ask.  I hope this helps!
> 
> 

Thank you very much !!
But now I have much weirder problem...
I got this error:

C:\>maillist.py
  File "C:\maillist.py", line 84

                                                                   ^
SyntaxError: invalid syntax

And the weird thing is that the program has only 83 lines...
For some reason python thinks that I have a ^ on the 84 code line.
Whats wrong ??

Thanks !

BTW, I didn't wrote this program.
I downloaded it (you can find the URL in my previous message) and
started to read it so I could make some changes in it...
-- 
1. The day Microsoft makes something that doesn't suck is probably the
day they start making vacuum cleaners.
2. Unix is user friendly - it's just picky about it's friends.
3. Documentation is like sex: when it is good, it is very, very good.
And when it is bad, it is better than nothing. - Dick Brandon