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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 line(self, x=None, y=None, **kwds):
 """ Plot DataFrame columns as lines. This function is useful to plot lines using DataFrame's values as coordinates. Parameters x : int or str, optional Columns to use for the horizontal axis. Either the location or the label of the columns to be used. By default, it will use the DataFrame indices. y : int, str, or list of them, optional The values to be plotted. Either the location or the label of the columns to be used. By default, it will use the remaining DataFrame numeric columns. **kwds Keyword arguments to pass on to :meth:`DataFrame.plot`. Returns ------- :class:`matplotlib.axes.Axes` or :class:`numpy.ndarray` Return an ndarray when ``subplots=True``. See Also -------- matplotlib.pyplot.plot : Plot y versus x as lines and/or markers. Examples -------- .. plot:: :context: close-figs The following example shows the populations for some animals over the years. .. plot:: :context: close-figs An example with subplots, so an array of axes is returned. <class 'numpy.ndarray'> .. plot:: :context: close-figs The following example shows the relationship between both populations. """

        return self(kind='line', x=x, y=y, **kwds)