Internals¶
How the magic of DirtyEquals.__eq__
works?¶
When you call x == y
, Python first calls x.__eq__(y)
. This would not help us
much, because we would have to keep an eye on order of the arguments when
comparing to DirtyEquals
objects. But that's where were another feature of
Python comes in.
When x.__eq__(y)
returns the NotImplemented
object, then Python will try to
call y.__eq__(x)
. Objects in the standard library return that value when they
don't know how to compare themselves to objects of type(y)
(Without checking
the C source I can't be certain if this assumption holds for all classes, but it
works for all the basic ones).
In pathlib.PurePath
you can see an example how that is implemented in Python.
By default, object implements
__eq__()
by usingis
, returningNotImplemented
in the case of a false comparison:True if x is y else NotImplemented
.
See the Python documentation for more information (object.__eq__
).