Is my implementation of happy number OK

[Cecil Westerhof]

I implemented happy_number function:
    _happy_set      = { '1' }
    _unhappy_set    = set()

    def happy_number(n):
        """
        Check if a number is a happy number
        https://en.wikipedia.org/wiki/Happy_number
        """

        def create_current(n):
            current_array = sorted([value for value in str(n) if value != '0'])
            return (current_array, ''.join(current_array))

        global _happy_set
        global _unhappy_set

        current_run         = set()
        current_array, \
            current_string  = create_current(n)
        if current_string in _happy_set:
            return True
        if current_string in _unhappy_set:
            return False
        while True:
            current_run.add(current_string)
            current_array, \
                current_string = create_current(sum([int(value) ** 2
                                                     for value in current_string]))
            if current_string in current_run | _unhappy_set:
                _unhappy_set |= current_run
                return False
            if current_string in _happy_set:
                _happy_set |= current_run
                return True

Besides it need some documentation: is it a good implementation? Or
are there things I should do differently?

To decide for the values from 1 to 1E8 if it is happy or not, takes
280 seconds. Not to bad I think. Also not very good.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof