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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_logo(fig, x=10, y=25, zorder=100, which='metpy', size='small', **kwargs):
 """Add the MetPy or Unidata logo to a figure. Adds an image to the figure. Parameters fig : `matplotlib.figure` The `figure` instance used for plotting x : int x position padding in pixels y : float y position padding in pixels zorder : int The zorder of the logo which : str Which logo to plot 'metpy' or 'unidata' size : str Size of logo to be used. Can be 'small' for 75 px square or 'large' for 150 px square. Returns ------- `matplotlib.image.FigureImage` The `matplotlib.image.FigureImage` instance created """

    fname_suffix = {'small': '_75x75.png',
                    'large': '_150x150.png'}
    fname_prefix = {'unidata': 'unidata',
                    'metpy': 'metpy'}
    try:
        fname = fname_prefix[which] + fname_suffix[size]
        fpath = posixpath.join('_static', fname)
    except KeyError:
        raise ValueError('Unknown logo size or selection')

    logo = imread(pkg_resources.resource_stream('metpy.plots', fpath))
    return fig.figimage(logo, x, y, zorder=zorder, **kwargs)