Apply suggestions from code review

Co-authored-by: Reuben Thomas-Davis <[email protected]>

slowapi/wrappers.py

@@ -29,6 +29,7 @@ def __init__(
  self.methods = methods
  self.error_message = error_message
  self.exempt_when = exempt_when
+ self._exempt_when_takes_request = len(inspect.signature(self.exempt_when).parameters) == 1
  self.cost = cost
  self.override_defaults = override_defaults
 
@@ -43,9 +44,7 @@ def is_exempt(self, request: Optional[Request] = None) -> bool:
  """
  if self.exempt_when is None:
  return False
- params = inspect.signature(self.exempt_when).parameters
- param_len = len(params)
- if param_len == 1 and request:
+ if self._exempt_when_takes_request and request:
  return self.exempt_when(request)
  return self.exempt_when()