<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_X0(X):
 """ Return zero-th element of a one-element data container. """

    if pandas_available and isinstance(X, pd.DataFrame):
        assert len(X) == 1
        x = np.array(X.iloc[0])
    else:
        x, = X
    return x