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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 pca_variance_ratio(adata, n_pcs=30, log=False, show=None, save=None):
 """Plot the variance ratio. Parameters n_pcs : `int`, optional (default: `30`) Number of PCs to show. log : `bool`, optional (default: `False`) Plot on logarithmic scale.. show : `bool`, optional (default: `None`) Show the plot, do not return axis. save : `bool` or `str`, optional (default: `None`) If `True` or a `str`, save the figure. A string is appended to the default filename. Infer the filetype if ending on {'.pdf', '.png', '.svg'}. """

    ranking(adata, 'uns', 'variance_ratio', n_points=n_pcs, dictionary='pca', labels='PC', log=log)
    utils.savefig_or_show('pca_variance_ratio', show=show, save=save)