Unit comparisons?

[quantumtrope]

I'm having trouble understanding what is compared between two quantities -- seems like only magnitudes?

import pint
ureg1 = pint.UnitRegistry()
ureg2 = pint.UnitRegistry()

ureg1 == ureg2
# >> False

q1 = ureg1.Quantity(0,"W")
q2 = ureg2.Quantity(0,"W")

q1 == q2
# >> True

# Still `True` if q1 and q2 have a non-zero value:
q1 = ureg1.Quantity(1,"W")
q2 = ureg2.Quantity(1,"W")

q1 == q2
# >> True

ureg1.Quantity == ureg2.Quantity
# >> False

q2.units == q1.units
# >> ValueError: Cannot operate with Unit and Unit of different registries.

q1.magnitude == q2.magnitude
# >> True

Is that meant to be the case? I would have expected that comparing two quantities from different registries would throw an error because their units don't match. What am I missing here?

[hgrecco]

Comparing units from different registries is not well-defined, and therefore it is an invalid operation. You should not expect a valid result. We rely on Python's consenting adults philosophy.

If you are interested in the details, to avoid a performance hit Quantity._eq__ compares q2._units == q1._units, not q2.units == q1.units

[quantumtrope]

Good reminder of pythons consenting adults philosophy here. I knew that it should fail, but I tried it anyway and was surprised by the result. The detail makes sense and I appreciate the peak under the curtain; I was trying to look through the source code but got lost in the breadcrumb trail.