Giving random.choice(seq) an empty sequence leads to a
misleading error message, as per this example:

>>> import random; random.choice([])
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.3/random.py", line 231, in choice
    return seq[int(self.random() * len(seq))]
IndexError: list index out of range


A simple fix is to "assert len(seq) > 0" in the choice
method.

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Perhaps I've been using it for too long, but I do not find
the error message to misleading.  Also, I like having this
method as simple and lightweight as possible though it may
be worthwhile to add a line to the docs, "If the sequence is
emtpy, raises a TypeError." 

If someone accepts this request, it should implemented as a
try/except rather than an assertion.  That approach would
also let you catch TypeErrors raised is the argument doesn't
define __len__ and __getitem__, for example: 
random.choice(set('abc'))

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Tim, I'm -1 on this one.  What do you think?

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No, I don't want to change this either.  choice() is one of the 
few library functions where speed matters a lot, and checking 
for invalid arguments *just* to give a wordier error message 
would be a losing tradeoff because of that.  If you want to 
add a line to the docs, that's cool, but not "If the sequence 
is empty, raises TypeError".  That's a bad idea because it 
actually raises IndexError <wink>.

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Added a line to the docs:
   Doc/lib/librandom.tex 1.38
Marking as closed.