<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fit(self, X):
 """Fit Kernel density estimation to an list of values. Args: X: 1-d `np.ndarray` or `pd.Series` or `list` datapoints to be estimated from. This function will fit a gaussian_kde model to a list of datapoints and store it as a class attribute. """


        self.constant_value = self._get_constant_value(X)

        if self.constant_value is None:
            self.model = scipy.stats.gaussian_kde(X)

        else:
            self._replace_constant_methods()

        self.fitted = True