``comparison-with-itself`` only flags comparison with Name

[harupy]

Question about the comparison-with-itself rule. Is there a reason this rule only flags comparison with Name (e.g. a == a)? Is it challenging to extend it to support any comparison where the left hand expression is equal to the right hand expression (e.g. a.b == a.b)?

[Pierre-Sassoulas]

Yes, probably lack of time and keeping it simple and stupid (the primer would confirm this if someone open a PR).

[jacobtylerwalls]

But what about:

class A:
  @property
  def now(self):
      return time.time()

a = A()
a.now == a.now  # False, not redundant

[Pierre-Sassoulas]

This should definitely not raise :

class A:
  @property
  def now(self):
      return time.time()

a = A()
start = a.now
start == a.now  # False, not redundant

But the sample with a.now == a.now is weird to me, in what situation could it be useful ?

[jacobtylerwalls]

It was just a fast quick, example, so you need to imagine other properties that are not idempotent:

@property
def maybe_increments():
  if sometimes:
    self._private_counter += 1
  return self._private_counter

if a.maybe_increments != a.maybe_increments:
  keep_processing()

I think this needs a proposal before we bless it.

[Pierre-Sassoulas]

Right thank you, still weird code looking wrong, but we could find someone to defend this approach.

So the reason (that we forgot but probably discussed at the time of implementation) is that checking if a class name is a property is costly compared to the benefit and that we favor false négatives over false positive.

I'm still +0.5 for this.

[jacobtylerwalls]

I'm unclear what the the proposal is. How are we going to check things other than Names?