def get_num_from_bond(bond_symbol: str) -> int:
    """Retrieves the bond multiplicity from a SMILES symbol representing
    a bond. If ``bond_symbol`` is not known, 1 is returned by default.

    :param bond_symbol: a SMILES symbol representing a bond.
    :return: the bond multiplicity of ``bond_symbol``, or 1 if
        ``bond_symbol`` is not recognized.
    """

    if bond_symbol == "=":
        return 2
    elif bond_symbol == "#":
        return 3
    else:
        return 1