Newbie Question: Sort Tip: Why n=n?

[Quinn Dunkan]

On Fri, 18 Jan 2002 00:49:46 -0500, Joshua Muskovitz <joshm at taconic.net> wrote:
>> def sortby(list, n):
>>     nlist = map(lambda x, n=n: (x[n], x), list)
>>     nlist.sort()
>>     return map(lambda (key, x): x, nlist)
>>
>> I understand everything about this except the n=n in the second line.
>> Does anyone know why this is required?
>
>Because the lambda function does not have access to 'n' directly.  So it
>declares a local 'n' that is set once at compile time to refer to the actual
>n.  (Essentially it caches the value of 'n'.)

In addition to simulating lexical scope, it's also an optimization trick,
because you can load locals faster than globals.