[Python-Dev] I'd like list.pop to accept an optional second argument giving a default value

[Jim Fulton]

I like the list pop method because it provides a way to use
lists as thread safe queues and stacks (since append and pop
are protected by the global interpreter lock).

With pop, you can essentially test whether the list is 
empty and get a value if it isn't in one atomic operation:

  try: 
      foo=queue.pop(0)
  except IndexError:
      ... empty queue case
  else:
      ... non-empty case, do something with foo

Unfortunately, this incurs exception overhead. I'd rather do 
something like:

  foo=queue.pop(0,marker)
  if foo is marker: 
      ... empty queue case
  else:
      ... non-empty case, do something with foo

I'd be happy to provide a patch.

Jim

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