Python 3.10 match case with arbitrary conditions

Question

Is there any way to use arbitrary conditions on cases in a Python 3.10+ match statement or is it necessary to fall back on if-then control structures?
Clarification: an arbitrary condition might be a function with myVariable as argument that evaluates to type bool.

The constraint here is to keep the order of the cases (since the first few cases appear extremely often and performance is essential).

match myVariable:
  case 'a': ...
  case someConditionOnMyVariable: ...
  case someOtherConditionOnMyVariable: ...
  case 'bb': ...
  case _: ...

Asked By: Waschbaer

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Source

Answer 1

If you mean the match statement, you could probably use a wildcard pattern with a guard for your arbitrary condition:

def check(x):
    return len(x) % 3 == 0


def test(my_var):
    match my_var:
        case 'a':
            print("aa!")
        case _ if check(my_var):
            print("yup!")
        case _:
            print("no match")


test("a")
test("bbb")
test("blop")

prints out

aa!
yup!
no match

Answered By: AKX

Python 3.10 match case with arbitrary conditions

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