Modified length specifiers: mapping between length modifiers and conversion specifiers. This generates all the
        possibilities, i.e. hhd, etc.

def _mod_spec(self):
        """
        Modified length specifiers: mapping between length modifiers and conversion specifiers. This generates all the
        possibilities, i.e. hhd, etc.
        """
        mod_spec={}

        for mod, sizes in self.int_len_mod.items():

            for conv in self.int_sign['signed']:
                mod_spec[mod + conv] = sizes[0]

            for conv in self.int_sign['unsigned']:
                mod_spec[mod + conv] = sizes[1]

        return mod_spec