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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lookup_sig(cls, sigs, method_name, expr_args, stmt_or_expr, context):
 """ Using a list of args, determine the most accurate signature to use from the given context """


        def synonymise(s):
            return s.replace('int128', 'num').replace('uint256', 'num')

        # for sig in sigs['self']
        full_sig = cls.get_full_sig(
            stmt_or_expr.func.attr,
            expr_args,
            None,
            context.custom_units,
            context.structs,
            context.constants,
        )
        method_names_dict = dict(Counter([x.split('(')[0] for x in context.sigs['self']]))
        if method_name not in method_names_dict:
            raise FunctionDeclarationException(
                "Function not declared yet (reminder: functions cannot "
                "call functions later in code than themselves): %s" % method_name
            )

        if method_names_dict[method_name] == 1:
            return next(
                sig
                for name, sig
                in context.sigs['self'].items()
                if name.split('(')[0] == method_name
            )
        if full_sig in context.sigs['self']:
            return context.sigs['self'][full_sig]
        else:
            synonym_sig = synonymise(full_sig)
            syn_sigs_test = [synonymise(k) for k in context.sigs.keys()]
            if len(syn_sigs_test) != len(set(syn_sigs_test)):
                raise Exception(
                    'Incompatible default parameter signature,'
                    'can not tell the number type of literal', stmt_or_expr
                )
            synonym_sigs = [(synonymise(k), v) for k, v in context.sigs['self'].items()]
            ssig = [s[1] for s in synonym_sigs if s[0] == synonym_sig]
            if len(ssig) == 0:
                raise FunctionDeclarationException(
                    "Function not declared yet (reminder: functions cannot "
                    "call functions later in code than themselves): %s" % method_name
                )
            return ssig[0]