Implementation of a symbol type in Python.

symbol.py

#!/usr/bin/env python

import unittest


class symbol(object):
    CACHE = {}

    def __new__(cls, name):
        if not isinstance(name, basestring):
            raise TypeError('argument `name` must be a string')

        if name not in symbol.CACHE:
            symbol.CACHE[name] = super(cls, symbol).__new__(cls, name)
        return symbol.CACHE[name]

    def __init__(self, name):
        self.name = name


class SymbolTest(unittest.TestCase):

    def test_create_symbol_not_equal(self):
        self.assertNotEqual(symbol('foo'), symbol('bar'))

    def test_create_symbol_equal(self):
        self.assertEqual(symbol('foo'), symbol('foo'))

    def test_create_symbol_with_number_name_raises_exception(self):
        with self.assertRaises(TypeError):
            symbol(42)

    def test_create_symbol_with_dict_name_raises_exception(self):
        with self.assertRaises(TypeError):
            symbol({'foo': 'bar'})

    def test_create_symbol_with_list_name_raises_exception(self):
        with self.assertRaises(TypeError):
            symbol(['foo', 'bar'])


if __name__ == '__main__':
    unittest.main()