Union(Interval(-oo, oo), FiniteSet(1)) not evaluated

[gxyd]

>>> Union(Interval(-oo, oo), FiniteSet(1))
(-∞, ∞) ∪ {1}       # this should return (-∞, ∞) i guess

Can some one please verify the validity of issue?

[jksuom]

I think it is valid. It seems to be caused by the confusion of booleans in FiniteSet._union on this line. (Interval(-oo, oo).contains(1) is True but not true.)

[gxyd]

In these situations why not use == instead of is? (I know the difference between is and ==). But would that be any of problem.

[gxyd]

I think it is valid. It seems to be caused by the confusion of booleans in FiniteSet._union on this line.

I also confirmed using git-bisect, the same conclusion.

[jksuom]

Perhaps other.contains(x) would suffice.

[jksuom]

This is from PEP 8:

Don't compare boolean values to True or False using == .

Yes: if greeting:
No: if greeting == True:
Worse: if greeting is True:

[gxyd]

>>> y, z = symbols('y z')
>>> if any(Interval(1, 2).contains(x) == True for x in [y, z]):
           print('yes')

None                    # expected behavior

while

>>> if any(Interval(1, 2).contains(x) for x in [y, z]):
           print('yes')

'yes'

I know why this is happening, i had the same situation in one of previous PR's. Do you think we should go with ==?.

[jksuom]

The docstring of contains says:
Returns True if 'other' is contained in 'self' as an element.
This looks to me as if saying that we can expect a boolean value or possibly None.

However, some internal _contains functions return boolean functions or true or false (singletons, I think). I have no clear idea about what should be done.

[gxyd]

.contains is supposed to return 3-valued logic True, False or None. This is different from in operator, which uses two valued-logic True, False and TypeError for unknown.

This looks to me as if saying that we can expect a boolean value or possibly None.

So i this is true what you said.

I am quoting @asmeurer here what he said in the is_convergent PR comment for is_convergent().

S.true should only be used in places where a general symbolic boolean could be returned. Also, since this uses three-valued logic (with None), it should use bool, since S.true only represents two-valued logic.

[leosartaj]

In the example given by @gxyd contains returns an unevaluated And because bound on x is not known. any returns True in this case. I think we should go with == here so that there is confusion.