def test_view_of_view(matrix_type, subset_func, subset_func2):
    adata = gen_adata((30, 15), X_type=matrix_type)
    adata.raw = adata
    if subset_func is single_subset:
        pytest.xfail("Other subset generating functions have trouble with this")
    var_s1 = subset_func(adata.var_names, min_size=4)
    var_view1 = adata[:, var_s1]
    var_s2 = subset_func2(var_view1.var_names)
    var_view2 = var_view1[:, var_s2]
    assert var_view2._adata_ref is adata
    obs_s1 = subset_func(adata.obs_names, min_size=4)
    obs_view1 = adata[obs_s1, :]
    obs_s2 = subset_func2(obs_view1.obs_names)
    assert adata[obs_s1, :][:, var_s1][obs_s2, :]._adata_ref is adata

    view_of_actual_copy = adata[:, var_s1].copy()[obs_s1, :].copy()[:, var_s2].copy()

    view_of_view_copy = adata[:, var_s1][obs_s1, :][:, var_s2].copy()

    assert_equal(view_of_actual_copy, view_of_view_copy, exact=True)
def _parse_filter():
        op = pyparsing.oneOf('! & |')
        lpar  = pyparsing.Literal('(').suppress()
        rpar  = pyparsing.Literal(')').suppress()

        k = pyparsing.Word(pyparsing.alphanums)
        # NOTE: We may need to expand on this list, but as this is not a real
        # LDAP server we should be OK.
        # Value to contain:
        #   numbers, upper/lower case letters, astrisk, at symbol, minus, full
        #   stop, backslash or a space
        v = pyparsing.Word(pyparsing.alphanums + "-*@.\\ äöü")
        rel = pyparsing.oneOf("= ~= >= <=")

        expr = pyparsing.Forward()
        atom = pyparsing.Group(lpar + op + expr + rpar) \
                            | pyparsing.Combine(lpar + k + rel + v + rpar)
        expr << atom + pyparsing.ZeroOrMore( expr )

        return expr