Using Python Web GET data

Question

I'm trying to pass information to a python page via the url. I have the following link text:

"<a href='complete?id=%s'>" % (str(r[0]))

on the complete page, I have this:

import cgi
def complete():
    form = cgi.FieldStorage()
    db = MySQLdb.connect(user="", passwd="", db="todo")
    c = db.cursor()
    c.execute("delete from tasks where id =" + str(form["id"]))
    return "<html><center>Task completed! Click <a href='/chris'>here</a> to go back!</center></html>"

The problem is that when i go to the complete page, i get a key error on "id". Does anyone know how to fix this?

EDIT
when i run cgi.test() it gives me nothing

I think something is wrong with the way i'm using the url because its not getting passed through.

its basically localhost/chris/complete?id=1

/chris/ is a folder and complete is a function within index.py

Am i formatting the url the wrong way?

If the error occurs when some form sends data to the Complete page, then you need to include the form in your question. It doesn't appear to have a field named id. — S.Lott
– S.Lott, Commented Dec 21, 2008 at 13:16
BTW, when changing server state (a SQL DELETE) it is considered best practice to use a POST (then a redirect), not a GET. — Daniel Naab
– Daniel Naab, Commented Dec 21, 2008 at 19:29
more info: theserverside.com/tt/articles/article.tss?l=RedirectAfterPost — Daniel Naab
– Daniel Naab, Commented Dec 21, 2008 at 19:33

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

The error means that form["id"] failed to find the key "id" in cgi.FieldStorage().

To test what keys are in the called URL, use cgi.test():

cgi.test()

Robust test CGI script, usable as main program. Writes minimal HTTP headers and formats all information provided to the script in HTML form.

EDIT: a basic test script (using the python cgi module with Linux path) is only 3 lines. Make sure you know how to run it on your system, then call it from a browser to check arguments are seen on the CGI side. You may also want to add traceback formatting with import cgitb; cgitb.enable().

#!/usr/bin/python
import cgi
cgi.test()

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 21, 2008 at 11:26

gimel

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Comments

mcrute · Accepted Answer · 2008-12-24 04:24:29Z

1

Have you tried printing out the value of form to make sure you're getting what you think you're getting? You do have a little problem with your code though... you should be doing form["id"].value to get the value of the item from FieldStorage. Another alternative is to just do it yourself, like so:

import os
import cgi

query_string = os.environ.get("QUERY_STRING", "")
form = cgi.parse_qs(query_string)

This should result in something like this:

{'id': ['123']}

answered Dec 24, 2008 at 4:24

mcrute

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Comments

Steen · Accepted Answer · 2008-12-21 11:32:46Z

0

First off, you should make dictionary lookups via

possibly_none = my_dict.get( "key_name" )

Because this assigns None to the variable, if the key is not in the dict. You can then use the

if key is not None:
    do_stuff

idiom (yes, I'm a fan of null checks and defensive programming in general...). The python documentation suggests something along these lines as well.

Without digging into the code too much, I think you should reference

form.get( 'id' ).value

in order to extract the data you seem to be asking for.

answered Dec 21, 2008 at 11:32

Steen

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3 Comments

gimel Over a year ago

The doc shows a cgi.FieldStorage() example: if not (form.has_key("name") and form.has_key("addr")): ...

The.Anti.9 Over a year ago

form.get( 'id' ).value doesn't work either. I get an attribute error. I think something is wrong with the way i'm using the url because its not getting passed through

gimel Over a year ago

to see what is being passed, use cgi.test()

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