23.07.19 23:59, Kristian Klette пише:
During the sprints after EuroPython, I made an attempt at adding support for
comparing the results from `.values()` of two dicts.
Currently the following works as expected:
```
d = {'a': 1234}
d.keys() == d.keys()
d.items() == d.items()
```
but `d.values() == d.values()` does not return the expected
results. It always returns `False`. The symmetry is a bit off.
Is it expected to you that `iter(d) == iter(d)` returns False?
By default the equality operator returns True when and only when
operands are identical. It is expected. Some objects (like numbers or
strings) can override the default behavior and implement different rules
for equality.
I'd argue that Python should compare the values as expected here,
or if we don't want to encourage that behaviour, maybe we should
consider raising an exception.
Returning just `False` seems a bit misleading.
What the rule for equality do you propose? What is the use case for it?
If you want to compare dict value views as ordered sequences, it can be
surprised that `d1.values() != d2.values()` when `d1 == d2`. It will be
inconsistent with orderless comparison of `keys()` and `items()`. If you
want to compare them as unordered sequences, the computation complexity
of the operation will be quadratic.
Note also, that while in Python 2 always `d.values() == d.values()`, it
is possible that `d1.keys() != d2.keys()` and `d1.values() !=
d2.values()` when `d1 == d2`. Python 3 is more consistent.
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