def _some_atoms_left(tokens, atoms, natoms):
    """
    Return True if the token list expected to contain atoms.

    If the number of atoms is known before hand, then the function compares the
    number of already found atoms to the expected number. If the '--' token if
    found, it is removed from the token list and there is no atom left.

    Parameters
    ----------
    tokens: collections.deque[str]
        Deque of token to inspect. The deque **can be modified** in place.
    atoms: list
        List of already found atoms.
    natoms: int or None
        The number of expected atoms if known, else None.

    Returns
    -------
    bool
    """
    if not tokens:
        return False
    if tokens and tokens[0] == '--':
        tokens.popleft()
        return False
    if natoms is not None and len(atoms) >= natoms:
        return False
    return True