def list_partial_circuits(circuit):
    """
    List the partial sub-circuits of `circuit`.

    The "parital circuits" are defined as
    the slices `circuit[0:n]` for `0 <= n <= len(circuit)`.

    Parameters
    ----------
    circuit : tuple of operation labels or Circuit
        The circuit to act upon.

    Returns
    -------
    list of Circuit objects.
        The parial circuits.
    """
    ret = []
    for l in range(len(circuit) + 1):
        ret.append(tuple(circuit[0:l]))
    return ret