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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_basemap(ax, zoom=12):
 """ Adds map to a plot. """

    url = ctx.sources.ST_TONER_LITE
    xmin, xmax, ymin, ymax = ax.axis()
    basemap, extent = ctx.bounds2img(xmin, ymin, xmax, ymax,
                                            zoom=zoom, url=url)
    ax.imshow(basemap, extent=extent, interpolation='bilinear')
    # restore original x/y limits
    ax.axis((xmin, xmax, ymin, ymax))