[Python-Dev] PEP 343 - multiple context managers in one statement

Tue Oct 25 22:40:30 CEST 2005

I have a deep suspicion that this has been done to death already, but
my searching ability isn't up to finding the reference. So I'll simply
ask the question, and not offer a long discussion:
Has the option of letting the with statement admit multiple context
managers been considered (and presumably rejected)?
I'm thinking of
 with expr1, expr2, expr3:
 # whatever
In some ways, this doesn't even need an extension to the PEP - giving
tuples suitable __enter__ and __exit__ methods would do it. Or, I
suppose a user-defined manager which combined a list of others:
 class combining:
 def __init__(*mgrs):
 self.mgrs = mgrs
 def __with__(self):
 return self
 def __enter__(self):
 return tuple(mgr.__enter__() for mgr in self.mgrs)
 def __exit__(self, type, value, tb):
 # first in, last out
 for mgr in reversed(self.mgrs):
 mgr.__exit__(type, value, tb)
Would that be worth using as an example in the PEP?
Sorry - it got a bit long anyway...
Paul.
PS The signature of __with__ in example 4 in the PEP is wrong - it has
an incorrect "lock" parameter.