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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 positive_int(string):
 """Convert string to positive integer."""

    error_msg = 'Positive integer required, {string} given.'.format(string=string)
    try:
        value = int(string)
    except ValueError:
        raise ArgumentTypeError(error_msg)
    if value < 0:
        raise ArgumentTypeError(error_msg)
    return value