Guido van Rossum <gu...@python.org> added the comment:
OK, that makes sense, it works similar to ChainMap.copy(), which copies maps[0]
and keeps links to the rest. So in particular `cm | {}` will do the same thing
as cm.copy().
Im not sure if the dict(other) cast is the best way to go about it. Maybe this
would work?
def __or__(self, other):
new = self.copy()
new |= other # OR new.update(other) ???
return new
def __ior__(self, other):
self.update(other)
return self
Note that there is no ChainMap.update() definition -- it relies on
MutableMapping.update().
I guess we need a __ror__ as well, in case there's some other mapping that
doesn't implement __or__:
def __ror__(self, other):
new = other.copy()
new.update(self)
return new
Note that this doesn't return a ChainMap but an instance of type(other). If
other doesn't have a copy() method it'll fail.
As a refinement, __or__ and __ror__ should perhaps check whether the operation
can possibly succeed and return NotImplemented instead of raising? (Based on
the type of other only, not its contents.)
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<https://bugs.python.org/issue36144>
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