Message376316
The operator override dunder methods, like `__add__`, are described in
the “Data model” docs here:
<https://docs.python.org/3.10/reference/datamodel.html#object.__add__>
Those docs say:
> For instance, to evaluate the expression `x + y`, where `x` is an
> instance of a class that has an `__add__()` method, `x.__add__(y)` is
> called.
But this is not correct: `x + y` always uses `type(x).__add__`, which
may be different from `x.__add__` if `__add__` has been set directly on
the instance.
Demonstration:
```
class C:
def __add__(self, other):
return "from class"
c = C()
print(c + c) # prints "from class"
c.__add__ = lambda other: "from instance"
print(c.__add__(c)) # prints "from instance"
print(type(c).__add__(c, c)) # prints "from class"
print(c + c) # prints "from class"!
```
The same issue appears in the reversed operator dunder (`__radd__`,
et al.) docs below.
I have a patch that I can submit as a PR; just need a bpo number. |
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Date |
User |
Action |
Args |
2020-09-03 20:30:50 | wchargin | set | recipients:
+ wchargin, docs@python |
2020-09-03 20:30:50 | wchargin | set | messageid: <1599165050.43.0.0605757296817.issue41706@roundup.psfhosted.org> |
2020-09-03 20:30:50 | wchargin | link | issue41706 messages |
2020-09-03 20:30:50 | wchargin | create | |
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