code: def pca_loadings(adata, components=None, show=None, save=None):
      
      if components is None: components = [1, 2, 3]
      elif isinstance(components, str): components = components.split(',')
      components = np.array(components) - 1
      ranking(adata, 'varm', 'PCs', indices=components)
      utils.savefig_or_show('pca_loadings', show=show, save=save)
docs: Rank genes according to contributions to PCs.
  
      Parameters
      ----------
      adata : :class:`~anndata.AnnData`
          Annotated data matrix.
      components : str or list of integers, optional
          For example, ``'1,2,3'`` means ``[1, 2, 3]``, first, second, third
          principal component.
      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'}.