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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 add_legend(self, labels=None, **kwargs):
 """Specify legend for a plot. Adds labels and basic legend specifications for specific plot. For the optional Args, refer to https://matplotlib.org/api/_as_gen/matplotlib.pyplot.legend.html for more information. # TODO: Add legend capabilities for Loss/Gain plots. This is possible using the return_fig_ax kwarg in the main plotting function. Args: labels (list of str):
 String representing each item in plot that will be added to the legend. Keyword Arguments: loc (str, int, len-2 list of floats, optional):
 Location of legend. See matplotlib documentation for more detail. Default is None. bbox_to_anchor (2-tuple or 4-tuple of floats, optional):
 Specify position and size of legend box. 2-tuple will specify (x,y) coordinate of part of box specified with `loc` kwarg. 4-tuple will specify (x, y, width, height). See matplotlib documentation for more detail. Default is None. size (float, optional):
 Set size of legend using call to `prop` dict in legend call. See matplotlib documentaiton for more detail. Default is None. ncol (int, optional):
 Number of columns in the legend. Note: Other kwargs are available. See: https://matplotlib.org/api/_as_gen/matplotlib.pyplot.legend.html """

        if 'size' in kwargs:
            if 'prop' not in kwargs:
                kwargs['prop'] = {'size': kwargs['size']}
            else:
                kwargs['prop']['size'] = kwargs['size']
            del kwargs['size']
        self.legend.add_legend = True
        self.legend.legend_labels = labels
        self.legend.legend_kwargs = kwargs
        return