Why does this work in jython and not in python?

[Jeremy Hylton]

On Wed, 2003-06-18 at 13:01, Roman Milner wrote:
> I'm sorting a list of dictionaries based on a particular key. Using
> the code below, the list gets sorted in jython, but not in python. I'm
> using python 2.2.1 and jython 2.1.
> 
> I really appreciate any help.
> 
> ^Roman
> 
> # if you run this with jython, you get a sorted list
> # with python the list stays in the same order. Why?
> 
> tdict = [{'a':5}, {'a':3},{'a':4},{'a':2},{'a':1}]
> 
> def sort_func(one, two):
>     return one['a'] < two['a']
> 
> print tdict
> tdict.sort(sort_func)
> print tdict

I don't understand why it works in jython.  The problem is that your
sort_func is returning the wrong value.

It should return -1 if one < two, 1 if one > two, and 0 if equal.  The
sort_func() will always report that two values are greater than or equal
to each other.  Try this instead:

def sort_func(one, two):
    return cmp(one["a"], two["a"])

Jeremy