code: def get_chromosomes(snps):
      
  
      if isinstance(snps, pd.DataFrame):
          return list(pd.unique(snps["chrom"]))
      else:
          return []
docs: Get the chromosomes of SNPs.
  
      Parameters
      ----------
      snps : pandas.DataFrame
  
      Returns
      -------
      list
          list of str chromosomes (e.g., ['1', '2', '3', 'MT'], empty list if no chromosomes