Given the current semantics of PEP 343 and the following class:
class null_context(object):
def __context__(self):
return self
def __enter__(self):
return self
def __exit__(self, *exc_info):
pass
Mistakenly writing:
with null_context:
# Oops, passed the class instead of an instance
Would give a less than meaningful error message:
TypeError: unbound method __context__() must be called with null_context
instance as first argument (got nothing instead)
It's the usual metaclass problem with invoking a slot (or slot equivalent) via
"obj.__slot__()" rather than via "type(obj).__slot__(obj)" the way the
underlying C code does.
I think we need to fix the proposed semantics so that they access the slots
via the type, rather than directly through the instance. Otherwise the slots
for the with statement will behave strangely when compared to the slots for
other magic methods.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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