Inconsistency in pattern matching involving `fractions.Fraction` objects

[MegaIng (Cornelius Krupp)]

@sr-murthy

In the docs we have this:

For example, if MyClass.__match_args__ is ("left", "center", "right") that means that case MyClass(x, y) is equivalent to case MyClass(left=x, center=y). Note that the number of arguments in the pattern must be smaller than or equal to the number of elements in match_args; if it is larger, the pattern match attempt will raise a TypeError.

Yes, this means that if one of the latter is chosen, the first doesn’t work. But if the first is chosen, the latter two have surprising semantics (matching only the numerator).

@Rosuav

This one, without a shadow of a doubt. What I’m less sure of is what would happen if someone tried to match with a single integer, and whether that would have sane semantics.

Yep! But that isn’t what OP wanted to do. And if __match_args__ was defined already, this would have silently introduced a bug that OP might not have noticed for a long time. Having to write out numerator and denominator forces you to think about the fact that you are doing component wise comparison. Also see this previous discussion that popped up in related topics: Missing `__match_args__` attribute for `Fraction`