def signature(self):
        """Return the signature of a first-class function.

        Returns
        -------
        sig : Signature
          The returned Signature instance represents the type of a
          first-class function that the given WrapperAddressProtocol
          instance represents.
        """
Return the signature of a first-class function.

        Returns
        -------
        sig : Signature
          The returned Signature instance represents the type of a
          first-class function that the given WrapperAddressProtocol
          instance represents.
        
numba/core/types/function_type.py