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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 apply_train(self, df:DataFrame):
 "Compute the means and stds of `self.cont_names` columns to normalize them." self.means,self.stds = {},{} for n in self.cont_names: assert is_numeric_dtype(df[n]), (f"""Cannot normalize '{n}' column as it isn't numerical. Are you sure it doesn't belong in the categorical set of columns?"""
)
            self.means[n],self.stds[n] = df[n].mean(),df[n].std()
            df[n] = (df[n]-self.means[n]) / (1e-7 + self.stds[n])