Cause of the problem A variable name in a case clause is treated as a name capture pattern. It always matches and tries to make an assignment to the variable name. This is almost certainly not what was intended. Because the first matching case wins and because case OKAY always matches, the other case clauses … Read more
Example converted to pattern matching Here’s the equivalent code using match and case: match x: case int(): pass case str(): x = int(x) case float() | Decimal(): x = round(x) case _: raise TypeError(‘Unsupported type’) Explanation PEP 634 specifies that isinstance() checks are performed with class patterns. To check for an instance of str, write … Read more
You can define a default case in Python. For this you use a wild card (_). The following code demonstrates it: x = “hello” match x: case “hi”: print(x) case “hey”: print(x) case _: print(“not matched”)
The key to the solution is to build a wrapper that overrides the __eq__ method and replaces it with an approximate match: import cmath class Approximately(complex): def __new__(cls, x, /, **kwargs): result = complex.__new__(cls, x) result.kwargs = kwargs return result def __eq__(self, other): try: return isclose(self, other, **self.kwargs) except TypeError: return NotImplemented It creates approximate … Read more
If the constant you’re testing against is a dotted name, then it should be treated as a constant instead of as the name of the variable to put the capture in (see PEP 636 # Matching against constants and enums): class Codes: SUCCESS = 200 NOT_FOUND = 404 def handle(retcode): match retcode: case Codes.SUCCESS: print(‘success’) … Read more