Improve in-place BinOp methods for sets #7161
Merged
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This PR proposes altering the annotations of four BinOp dunder methods for set classes, so that they return
Self
. The four methods in question are:__ior__
__ixor__
__iand__
__isub__
I have several reasons for proposing this change:
__ior__
and__ixor__
are unsafe. If I have a sets = {1, 2}
it has typeset[int]
, but if I then dos |= {'foo', 'bar'}
, the type of the variable has mutated fromset[int]
toset[str | int]
.Result type of | incompatible in assignment
. If type checkers are going to balk at this kind of thing anyway, then we may as well improve the error message.set
: these methods do, in fact, returnself
at runtime.Self
.typing.AbstractSet
ortyping.MutableSet
to return anything exceptSelf
from any of these methods, given that they update the object in-place.For those who (like me) haven't got their
set
operations memorized, here's a rundown I made for myself...__ior__
|=
.update()
__ixor__
^=
.symmetric_difference_update()
__iand__
&=
.intersection_update()
__isub__
-=
.difference_update()