Pulling all n-sized combinations from a list

[jess.austin at gmail.com]

hi,

I'm not sure why this hasn't come up yet, but this seems to beg for
list comprehensions, if not generator expressions.  All of the
following run in under 2 seconds on my old laptop:

>>> alph = 'abcdefghijklmnopqrstuvwxyz'
>>> len([''.join((a,b,c,d)) for a in alph for b in alph for c in alph for d in alph])
456976
>>> len([''.join((a,b,c,d)) for a in alph for b in alph for c in alph for d in alph
...      if (a>=b and b>=c and c>=d)])
23751
>>> len([''.join((a,b,c,d)) for a in alph for b in alph for c in alph for d in alph
...      if (a!=b and b!=c and c!=d and d!=a and b!=d and a!=c)])
358800
>>> len([''.join((a,b,c,d)) for a in alph for b in alph for c in alph for d in alph
...      if (a>b and b>c and c>d)])
14950

cheers,
Jess