17.02.20 23:02, Guido van Rossum пише:
Now that the last bits of discussion about PEP 584 have been settled (we
will *not* be calling the `copy` or `update` methods) I am accepting
this PEP. Congratulations Steven and Brandt!
Thanks to everyone else who gave their opinion.
Formally, I will just send my recommendation to accept the PEP to the
Steering Council -- they will then let us know whether they agree, and
once that's done we can update the PEP with the "Accepted" status and
land the implementation (https://github.com/python/cpython/pull/12088).
(Hm, the PEP should probably also link to that PR rather than to
Brandt's private branch.)
Comments to the PEP.
In the disadvantages of existing syntax `{**d1, **d2}`
(https://www.python.org/dev/peps/pep-0584/#d1-d2) it claims:
{**d1, **d2} ignores the types of the mappings and always returns a dict.
type(d1)({**d1, **d2}) fails for dict subclasses such as defaultdict that have
an incompatible __init__ method.
But it was decided that `d1 | d2` also should ignore the types of the
operands and always return a dict. And it accepts only dicts, not
general mappings, in difference to `{**d1, **d2}`.
So the only disadvantage of `{**d1, **d2}` is that it is not well known
and "looks ugly". But it supports general mappings.
There is a similar note about ChainMap
(https://www.python.org/dev/peps/pep-0584/#collections-chainmap)
Like dict unpacking, it is tricky to get it to honor the desired subclass. For
the same reason, type(d1)(ChainMap(d2, d1)) fails for some subclasses of dict.
which is not relevant to the final implementation of PEP 584.
The pure-Python implementation of the non-inplace operator can be
simpler if use dict unpacking:
def __or__(self, other):
if not isinstance(other, dict):
return NotImplemented
return {**self, **other}
def __ror__(self, other):
if not isinstance(other, dict):
return NotImplemented
return {**other, **self}
I suggest to include to objections that non-inplace merging of two dicts
is much less common operation than concatenating of two strings or other
sequences, and that the existing syntax `{**d1, **d2}` completely
satisfies the need. The in-place operator is completely equivalent to
dict.update(). So the possible benefit of adding support of two
operators for dict is much less than common bar for changes in the
builtin types.
This is why I still -0 for this feature. In the initial form it
contradicted the behavior of other builtin types and operators, but
after fixing contradictions it became pretty useless.
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