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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 fit(self, range, function=None):
 """Fits a function to the active display's data trace within a specified range of the time window. E.g.:: # Fit's a gaussian to the first 30% of the time window. lockin.fit(range=(0, 30), function='gauss') :param start: The left limit of the time window in percent. :param stop: The right limit of the time window in percent. :param function: The function used to fit the data, either 'line', 'exp', 'gauss' or None, the default. The configured fit function is left unchanged if function is None. .. note:: Fitting takes some time. Check the status byte to see when the operation is done. A running scan will be paused until the fitting is complete. .. warning:: The SR850 will generate an error if the active display trace is not stored when the fit command is executed. """

        if function is not None:
            self.fit_function = function
        cmd = 'FITT', Integer(min=0, max=100), Integer(min=0, max=100)
        self._write(cmd, start, stop)