def _protein_dict(pep_lst):
    # region
    """
    Create a dictionary:
        key = protein id
        value = list of peptides associated with protein    )

    Dictionary gives us the raw count of unique peptide count for each protein.

    Parameters
    ----------
    pep_lst

    Returns
    -------
    dictionary

    """
    # endregion
    protein_dict = dict()
    for peptide_id, proteins in pep_lst:
        for protein_id in proteins:
            p_id = int(protein_id)
            if p_id not in protein_dict:
                protein_dict[p_id] = []
            protein_dict[p_id].append(int(peptide_id))
    return protein_dict