On Wed, Nov 15, 2017 at 5:37 PM, Nick Coghlan ncoghlan@gmail.com wrote:

On 16 November 2017 at 00:20, Jim J. Jewett jimjjewett@gmail.com wrote:

...

I *think* the following will happen:

"NewList[int]" will be evaluated, and __class_getitem__ called, so

that the bases tuple will be (A, GenericAlias(NewList, int), B)

# (A)  I *think* __mro_entries__ gets called with the full tuple,
# instead of just the object it is found on.
# (B) I *think* it is called on the results of evaluating
# the terms within the tuple, instead of the original
# string representation.
_tmp = __mro_entries__(A, GenericAlias(NewList, int), B)

# (C)  I *think* __mro_entries__ returns a replacement for
# just the single object, even though it was called on
# the whole tuple, without knowing which object it
# represents.
bases = (A, _tmp, B)

My understanding of the method signature:

def __mro_entries__(self, orig_bases):
    ...
    return replacement_for_self

My assumption as to the purpose of the extra complexity was:

• given orig_bases, a method could avoid injecting bases already listed if

it wanted to

• allowing multiple items to be returned provides a way to

programmatically combine mixins without having to define a new subclass for each combination

​Thanks, this might provide an answer to my question about multiple mro entries here

https://mail.python.org/pipermail/python-ideas/2017-November/047897.html%E2%...

​––Koos​