Errorratio.py

def printer_error(s):
    """
    In a factory a printer prints labels for boxes. For one kind of boxes the printer has to use colors which, for the sake of simplicity, are named with letters from a to m.
    The colors used by the printer are recorded in a control string. For example a "good" control string would be aaabbbbhaijjjm meaning that the printer used three times color a, four times color b, one time color h then one time color a...
    Sometimes there are problems: lack of colors, technical malfunction and a "bad" control string is produced e.g. aaaxbbbbyyhwawiwjjjwwm with letters not from a to m.
    You have to write a function printer_error which given a string will output the error rate of the printer as a string representing a rational whose numerator is the number of errors and the denominator the length of the control string. Don't reduce this fraction to a simpler expression.
    The string has a length greater or equal to one and contains only letters from ato z.

    #Examples:
    s="aaabbbbhaijjjm"
    error_printer(s) => "0/14"

    s="aaaxbbbbyyhwawiwjjjwwm"
    error_printer(s) => "8/22"
    """
    return '{}/{}'.format( sum( 1 for c in s if ord(c) in range(ord('n'), ord('z') +1)) ,len(s))

if __name__ == "__main__":
    print(printer_error("aaabbbbhaijjjm"))
    print(printer_error("aaaxbbbbyyhwawiwjjjwwm"))