Always evaluate the signature when __signature__ is specified as a string.

Author: lucaswiman

src/makefun/main.py

@@ -246,11 +246,6 @@ def create_function(func_signature,             # type: Union[str, Signature]
     if isinstance(func_signature, str):
         # transform the string into a Signature and make sure the string contains ":"
         func_name_from_str, func_signature, func_signature_str = get_signature_from_string(func_signature, evaldict)
-        # If the signature is specified as a string, `__signature__` will not be correct in this case, since it
-        # will be a string. If it was computed in some other fashion (i.e. is an instance of inspect.Signature),
-        # then there is no need to update it.
-        if '__signature__' in attrs:
-            attrs['__signature__'] = func_signature
 
         # if not explicitly overridden using `func_name`, the name in the string takes over
         if func_name_from_str is not None:
@@ -283,6 +278,11 @@ def create_function(func_signature,             # type: Union[str, Signature]
     else:
         raise TypeError("Invalid type for `func_signature`: %s" % type(func_signature))
 
+    if isinstance(attrs.get('__signature__'), str):
+        # __signature__ must be a Signature object, so if it is a string,
+        # we need to evaluate it.
+        attrs['__signature__'] = get_signature_from_string(attrs['__signature__'], evaldict)[1]
+
     # extract all information needed from the `Signature`
     params_to_kw_assignment_mode = get_signature_params(func_signature)
     params_names = list(params_to_kw_assignment_mode.keys())