Demonstration of an idea:

pip install sigdepsem

Python 3.8 required.

Signature Dependent Semantics

There are two goals to the proposal:

1. Maintain nearly all backward compatibility for all item dunder methods even when using the signature_dependent_semantics decorator.

   >>> from sigdepsem import signature_dependent_semantics as sds
   >>> @sds
   ... class C:
   ...     def __init__(self, name):
   ...         self.name = name
   ...     def __getitem__(self, key):
   ...         return f"{(*key,)}"
   ...     def __setitem__(self, key, value):
   ...         self.set = f"{self.name}[{(*key,)}] = {value}"
   ...     def __delitem__(self, key):
   ...         self.del_ = f"del {self.name}[{(*key,)}]"
   ... 
   >>> C("c")[1,2,3]
   '(1, 2, 3)'

2. Allow for an optional change to the semantic meaning of the signatures of __getitem__, __setitem, __delitem__ such that the semantic meaning is more consistent with regular function calls.

   Example:

   >>> from sigdepsem import signature_dependent_semantics as sds
   >>> @sds
   ... class MyMapping:
   ...    # note the unusual __getitem__ signature that looks more like the
   ...    # signature of a regular callable (3 positional arguments)
   ...    def __getitem__(self, a, b, c):
   ...        return a, b, c
   ... 
   >>> 
   >>> m = MyMapping()
   >>> 
   >>> m[1,2,3]
   (1, 2, 3)
   >>> m[1,2,3,4]
   ...
   TypeError: __getitem__() takes 4 positional arguments but 5 were given