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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 _load_knownGene(filename):
 """ Load UCSC knownGene table. Parameters filename : str path to knownGene file Returns ------- df : pandas.DataFrame knownGene table if loading was successful, else None """

        try:
            df = pd.read_table(
                filename,
                names=[
                    "name",
                    "chrom",
                    "strand",
                    "txStart",
                    "txEnd",
                    "cdsStart",
                    "cdsEnd",
                    "exonCount",
                    "exonStarts",
                    "exonEnds",
                    "proteinID",
                    "alignID",
                ],
                index_col=0,
            )
            df["chrom"] = df["chrom"].str[3:]
            return df
        except Exception as err:
            print(err)
            return None