Which JSON module can I use in Python 2.5?

You can use simplejson.

As shown by the answer form pkoch you can use the following import statement to get a json library depending on the installed python version:

try:
    import json
except ImportError:
    import simplejson as json 

To Wells and others:

Way late here, but how can you write a script to import either json or simplejson depending on the installed python version?

Here's how:

try:
    import json
except ImportError:
    import simplejson as json 

I wrote the cjson 1.0.6 patch and my advice is don't use cjson -- there are other problems with cjson in how it handles unicode etc. I don't think the speed of cjson is worth dealing with the bugs -- encoding/decoding json is usually a very small bit of the time needed to process a typical web request...

json in python 2.6+ is basically simplejson brought into the standard library I believe...

I prefer cjson since it's much faster: http://www.vazor.com/cjson.html

json is a built-in module, you don't need to install it with pip.