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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 parsehours (hrstr):
 """Parse a string formatted as sexagesimal hours into an angle. This function converts a textual representation of an angle, measured in hours, into a floating point value measured in radians. The format of *hrstr* is very limited: it may not have leading or trailing whitespace, and the components of the sexagesimal representation must be separated by colons. The input must therefore resemble something like ``"12:34:56.78"``. A :exc:`ValueError` will be raised if the input does not resemble this template. Hours greater than 24 are not allowed, but negative values are. """

    hr = _parsesexagesimal (hrstr, 'hours', False)
    if hr >= 24:
        raise ValueError ('illegal hour specification: ' + hrstr)
    return hr * H2R