All combinations of a list

[Stephen Kloder]

June Kim wrote:

> Below is my first version of doing it:
>
> def comb(list):
>     if len(list) ==0:
>            return [[]]
>     return [ [[list[0]],[]][i]+c for i in (0,1) \
>            for c in comb(list[1:]) ]
>
> That works fine, but why does another version using
> lambda give a subscription error?
>
> def comb(list):
>     if len(list) ==0:
>            return [[]]
>     return  map(lambda x: [list[0]]+x , comb(list[1:]))  \
>              + comb(list[1:])
>
> Thanks in advance.
>
> June
>
> [This thread was first started from permutation lists
> and now that the topic has moved somewhat far from
> the originator's question, I open up this thread as a new one]

It does not work because list is not defined as a list inside the
context of lambda.  If you had not used a pre-defined name, the error
message would have been NameError.  Changing the last line to:
    return  map(lambda x,list=list: [list[0]]+x , comb(list[1:]))  \
             + comb(list[1:])
should do the job.

--
Stephen Kloder               |   "I say what it occurs to me to say.
stephenk at cc.gatech.edu       |      More I cannot say."
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