[Tutor] CGI Calculator

Mon Jul 16 18:50:19 CEST 2007

Darren Williams wrote:
> Hi all,
>  
> I am a Python convert coming from a JavaScript background

Welcome to Python, Darren.

> (as you can probably tell) and am currently writing my first 
> application using Python which will be a calculator for an online game 
> I used to play (thought it would be a decent first project) but am not 
> sure on the syntax for referencing an HTML form input field, I tried 
> this (which returns an error) -
>  
> XHTML form -
>  
> <?xml version="1.0" encoding="UTF-8"?>
> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
> "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
> <head>
>     <title>DopeWars Junkie Calculator</title>
> </head>
> <body>
>     <center>
>     <form method="post" action="http://newspyn.com/cgi-bin/JunkieCalc.py">
>         <p><b>Coat Size:</b>&#32;<input type="text" name="coatSize">
>         <p><b>Used Pockets:</b>&#32;<input type="text" name="usedPockets">
>         <p><b>Lab Space:</b>&#32;<input type="text" name="labSpace">
>         <p><b>Total Junkies:</b>&#32;<input type="text" 
> name="totalJunkies">
>         <p><b>Dealer Visits Remaining:</b>&#32;<input type="text" 
> name="DVR">
>         <p><input type="submit" value="Submit">
>     </form>
> </body>
> </html>
>  
> junkieCalc.py -
>  
> #!/usr/bin/env python
>  
> import cgi
>  
> def main():
>     print "Content-type: text/html\n"
>     form = cgi.FieldStorage()
>     if form.has_key("coatSize") and form.has_key("usedPockets") and 
> form.has_key("labSpace") and form.has_key("totalJunkies") and 
> form.has_key("DVR") and form["coatSize"].value != "" and 
> form["usedPockets"].value != "" and form["labSpace"].value != "" and 
> form["totalJunkies"].value != "" and form["DVR"].value != "":
>         Tokens = 0
>     while usedPockets > (totalJunkies - labSpace) * 17:
>         Tokens = Tokens + 1
>         usedPockets = (usedPockets - totalJunkies + labSpace) * 17
>         totalJunkies = totalJunkies + 1
>         print "Tokens"
>     else:
>         print "Try again"
>  
> main()
>  
> This is the error i'm getting -
>  
> Traceback (most recent call last): File 
> "D:\inetpub\vhosts\newspyn.com\cgi-bin\JunkieCalc.py", line 23, in ? 
> main() File "D:\inetpub\vhosts\newspyn.com\cgi-bin\JunkieCalc.py", 
> line 10, in main while usedPockets > (totalJunkies - labSpace) * 17: 
> UnboundLocalError: local variable 'usedPockets' referenced before 
> assignment

So, you get an error on line 10, which is:

while usedPockets > (totalJunkies - labSpace) * 17:

and it says that your variable is referenced before assignment.  Have 
you assigned a value to it?  In your intro you ask how to reference an 
HTML form field, well you're already doing it in your if statement: 
form["labSpace"].value, so if you want a local variable named 
usedPockets, you should assign a value to it, like:  usedPockets = 
form["usedPockets"].value

As an aside, a nice tool for helping debug CGI scripts is the CGI 
Traceback module.  Add this as the first line of the program (after the 
shebang line, before the import cgi:

import cgitb; cgitb.enable()

Hope that helps,
e.

>  
> Thanks in advance for any help :)
> ------------------------------------------------------------------------
>
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