On Sat, Jul 11, 2020 at 5:58 PM Chris Angelico <rosuav@gmail.com> wrote:
On Sun, Jul 12, 2020 at 10:30 AM Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:
Just had another thought about marking assignment targets.
The PEP currently forbids repeating bound names in a pattern to avoid raising expectations that
case Point(x, x):
would match only if the two arguments were equal.
But if assignment targets were marked, we could write this as
case Point(?x, x):
and it would work as expected.
Hang on. Matching happens before assignment, so this should use the previous value of x for the matching. At least, that's my understanding. If you do something like:
case Point(x, 2):
it won't assign x unless the second coordinate is 2, right?
Good catch. That's actually undefined -- we want to let the optimizer have some leeway in how to generate the best code for matching. See https://www.python.org/dev/peps/pep-0622/#performance-considerations Currently it doesn't optimize all that much -- it just processes patterns from left to right: ```
match Point(3, 3): ... case Point(x, 42): pass ... print(x) 3
--
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*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>