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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 head_circumference(return_X_y=True):
 """head circumference for dutch boys Parameters return_X_y : bool, if True, returns a model-ready tuple of data (X, y) otherwise, returns a Pandas DataFrame Returns ------- model-ready tuple of data (X, y) OR Pandas DataFrame Notes ----- X contains the age in years of each patient. y contains the head circumference in centimeters """

    # y is real
    # recommend ExpectileGAM
    head = pd.read_csv(PATH + '/head_circumference.csv', index_col=0).astype(float)
    if return_X_y:
        y = head['head'].values
        X = head[['age']].values
        return _clean_X_y(X, y)
    return head