def METHOD_NAME(mols, fasta_file):
    fasta_seqs = utils.fasta_dict_from_file(fasta_file)
    for mol_id in mols:
        # check if the FASTA file provides sequence for this
        if mol_id in fasta_seqs:
            mol = mols[mol_id]
            mol.residues = fasta_seqs[mol_id]['s']
            mol.length   = len(mol.residues)