diff --git a/pandas/tests/copy_view/__init__.py b/pandas/tests/copy_view/__init__.py new file mode 100644 index 0000000000000..e69de29bb2d1d diff --git a/pandas/tests/copy_view/test_indexing.py b/pandas/tests/copy_view/test_indexing.py new file mode 100644 index 0000000000000..16cd72cc1cb06 --- /dev/null +++ b/pandas/tests/copy_view/test_indexing.py @@ -0,0 +1,649 @@ +import numpy as np +import pytest + +import pandas as pd +from pandas import ( + DataFrame, + Series, +) +import pandas._testing as tm +import pandas.core.common as com +from pandas.tests.copy_view.util import get_array + +# ----------------------------------------------------------------------------- +# Indexing operations taking subset + modifying the subset/parent + + +def test_subset_column_selection(using_copy_on_write): + # Case: taking a subset of the columns of a DataFrame + # + afterwards modifying the subset + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + + subset = df[["a", "c"]] + + if using_copy_on_write: + # the subset shares memory ... + assert np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + # ... but uses CoW when being modified + subset.iloc[0, 0] = 0 + else: + assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + # INFO this no longer raise warning since pandas 1.4 + # with pd.option_context("chained_assignment", "warn"): + # with tm.assert_produces_warning(com.SettingWithCopyWarning): + subset.iloc[0, 0] = 0 + + assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + + expected = DataFrame({"a": [0, 2, 3], "c": [0.1, 0.2, 0.3]}) + tm.assert_frame_equal(subset, expected) + tm.assert_frame_equal(df, df_orig) + + +def test_subset_column_selection_modify_parent(using_copy_on_write): + # Case: taking a subset of the columns of a DataFrame + # + afterwards modifying the parent + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + + subset = df[["a", "c"]] + if using_copy_on_write: + # the subset shares memory ... + assert np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + # ... but parent uses CoW parent when it is modified + df.iloc[0, 0] = 0 + + assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + if using_copy_on_write: + # different column/block still shares memory + assert np.shares_memory(get_array(subset, "c"), get_array(df, "c")) + + expected = DataFrame({"a": [1, 2, 3], "c": [0.1, 0.2, 0.3]}) + tm.assert_frame_equal(subset, expected) + + +def test_subset_row_slice(using_copy_on_write): + # Case: taking a subset of the rows of a DataFrame using a slice + # + afterwards modifying the subset + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + + subset = df[1:3] + subset._mgr._verify_integrity() + + assert np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + + if using_copy_on_write: + subset.iloc[0, 0] = 0 + assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a")) + + else: + # INFO this no longer raise warning since pandas 1.4 + # with pd.option_context("chained_assignment", "warn"): + # with tm.assert_produces_warning(com.SettingWithCopyWarning): + subset.iloc[0, 0] = 0 + + subset._mgr._verify_integrity() + + expected = DataFrame({"a": [0, 3], "b": [5, 6], "c": [0.2, 0.3]}, index=range(1, 3)) + tm.assert_frame_equal(subset, expected) + if using_copy_on_write: + # original parent dataframe is not modified (CoW) + tm.assert_frame_equal(df, df_orig) + else: + # original parent dataframe is actually updated + df_orig.iloc[1, 0] = 0 + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"] +) +def test_subset_column_slice(using_copy_on_write, using_array_manager, dtype): + # Case: taking a subset of the columns of a DataFrame using a slice + # + afterwards modifying the subset + single_block = (dtype == "int64") and not using_array_manager + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)} + ) + df_orig = df.copy() + + subset = df.iloc[:, 1:] + subset._mgr._verify_integrity() + + if using_copy_on_write: + assert np.shares_memory(get_array(subset, "b"), get_array(df, "b")) + + subset.iloc[0, 0] = 0 + assert not np.shares_memory(get_array(subset, "b"), get_array(df, "b")) + + else: + # we only get a warning in case of a single block + warn = com.SettingWithCopyWarning if single_block else None + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(warn): + subset.iloc[0, 0] = 0 + + expected = DataFrame({"b": [0, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}) + tm.assert_frame_equal(subset, expected) + # original parent dataframe is not modified (also not for BlockManager case, + # except for single block) + if not using_copy_on_write and (using_array_manager or single_block): + df_orig.iloc[0, 1] = 0 + tm.assert_frame_equal(df, df_orig) + else: + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"] +) +@pytest.mark.parametrize( + "row_indexer", + [slice(1, 2), np.array([False, True, True]), np.array([1, 2])], + ids=["slice", "mask", "array"], +) +@pytest.mark.parametrize( + "column_indexer", + [slice("b", "c"), np.array([False, True, True]), ["b", "c"]], + ids=["slice", "mask", "array"], +) +def test_subset_loc_rows_columns( + dtype, row_indexer, column_indexer, using_array_manager +): + # Case: taking a subset of the rows+columns of a DataFrame using .loc + # + afterwards modifying the subset + # Generic test for several combinations of row/column indexers, not all + # of those could actually return a view / need CoW (so this test is not + # checking memory sharing, only ensuring subsequent mutation doesn't + # affect the parent dataframe) + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)} + ) + df_orig = df.copy() + + subset = df.loc[row_indexer, column_indexer] + + # modifying the subset never modifies the parent + subset.iloc[0, 0] = 0 + + expected = DataFrame( + {"b": [0, 6], "c": np.array([8, 9], dtype=dtype)}, index=range(1, 3) + ) + tm.assert_frame_equal(subset, expected) + # a few corner cases _do_ actually modify the parent (with both row and column + # slice, and in case of ArrayManager or BlockManager with single block) + if ( + isinstance(row_indexer, slice) + and isinstance(column_indexer, slice) + and (using_array_manager or dtype == "int64") + ): + df_orig.iloc[1, 1] = 0 + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"] +) +@pytest.mark.parametrize( + "row_indexer", + [slice(1, 3), np.array([False, True, True]), np.array([1, 2])], + ids=["slice", "mask", "array"], +) +@pytest.mark.parametrize( + "column_indexer", + [slice(1, 3), np.array([False, True, True]), [1, 2]], + ids=["slice", "mask", "array"], +) +def test_subset_iloc_rows_columns( + dtype, row_indexer, column_indexer, using_array_manager +): + # Case: taking a subset of the rows+columns of a DataFrame using .iloc + # + afterwards modifying the subset + # Generic test for several combinations of row/column indexers, not all + # of those could actually return a view / need CoW (so this test is not + # checking memory sharing, only ensuring subsequent mutation doesn't + # affect the parent dataframe) + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)} + ) + df_orig = df.copy() + + subset = df.iloc[row_indexer, column_indexer] + + # modifying the subset never modifies the parent + subset.iloc[0, 0] = 0 + + expected = DataFrame( + {"b": [0, 6], "c": np.array([8, 9], dtype=dtype)}, index=range(1, 3) + ) + tm.assert_frame_equal(subset, expected) + # a few corner cases _do_ actually modify the parent (with both row and column + # slice, and in case of ArrayManager or BlockManager with single block) + if ( + isinstance(row_indexer, slice) + and isinstance(column_indexer, slice) + and (using_array_manager or dtype == "int64") + ): + df_orig.iloc[1, 1] = 0 + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "indexer", + [slice(0, 2), np.array([True, True, False]), np.array([0, 1])], + ids=["slice", "mask", "array"], +) +def test_subset_set_with_row_indexer(indexer_si, indexer, using_copy_on_write): + # Case: setting values with a row indexer on a viewing subset + # subset[indexer] = value and subset.iloc[indexer] = value + df = DataFrame({"a": [1, 2, 3, 4], "b": [4, 5, 6, 7], "c": [0.1, 0.2, 0.3, 0.4]}) + df_orig = df.copy() + subset = df[1:4] + + if ( + indexer_si is tm.setitem + and isinstance(indexer, np.ndarray) + and indexer.dtype == "int" + ): + pytest.skip("setitem with labels selects on columns") + + if using_copy_on_write: + indexer_si(subset)[indexer] = 0 + else: + # INFO iloc no longer raises warning since pandas 1.4 + warn = com.SettingWithCopyWarning if indexer_si is tm.setitem else None + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(warn): + indexer_si(subset)[indexer] = 0 + + expected = DataFrame( + {"a": [0, 0, 4], "b": [0, 0, 7], "c": [0.0, 0.0, 0.4]}, index=range(1, 4) + ) + tm.assert_frame_equal(subset, expected) + if using_copy_on_write: + # original parent dataframe is not modified (CoW) + tm.assert_frame_equal(df, df_orig) + else: + # original parent dataframe is actually updated + df_orig[1:3] = 0 + tm.assert_frame_equal(df, df_orig) + + +def test_subset_set_with_mask(using_copy_on_write): + # Case: setting values with a mask on a viewing subset: subset[mask] = value + df = DataFrame({"a": [1, 2, 3, 4], "b": [4, 5, 6, 7], "c": [0.1, 0.2, 0.3, 0.4]}) + df_orig = df.copy() + subset = df[1:4] + + mask = subset > 3 + + if using_copy_on_write: + subset[mask] = 0 + else: + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(com.SettingWithCopyWarning): + subset[mask] = 0 + + expected = DataFrame( + {"a": [2, 3, 0], "b": [0, 0, 0], "c": [0.20, 0.3, 0.4]}, index=range(1, 4) + ) + tm.assert_frame_equal(subset, expected) + if using_copy_on_write: + # original parent dataframe is not modified (CoW) + tm.assert_frame_equal(df, df_orig) + else: + # original parent dataframe is actually updated + df_orig.loc[3, "a"] = 0 + df_orig.loc[1:3, "b"] = 0 + tm.assert_frame_equal(df, df_orig) + + +def test_subset_set_column(using_copy_on_write): + # Case: setting a single column on a viewing subset -> subset[col] = value + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + subset = df[1:3] + + if using_copy_on_write: + subset["a"] = np.array([10, 11], dtype="int64") + else: + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(com.SettingWithCopyWarning): + subset["a"] = np.array([10, 11], dtype="int64") + + subset._mgr._verify_integrity() + expected = DataFrame( + {"a": [10, 11], "b": [5, 6], "c": [0.2, 0.3]}, index=range(1, 3) + ) + tm.assert_frame_equal(subset, expected) + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"] +) +def test_subset_set_column_with_loc(using_copy_on_write, using_array_manager, dtype): + # Case: setting a single column with loc on a viewing subset + # -> subset.loc[:, col] = value + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)} + ) + df_orig = df.copy() + subset = df[1:3] + + if using_copy_on_write: + subset.loc[:, "a"] = np.array([10, 11], dtype="int64") + else: + with pd.option_context("chained_assignment", "warn"): + # The (i)loc[:, col] inplace deprecation gets triggered here, ignore those + # warnings and only assert the SettingWithCopyWarning + raise_on_extra_warnings = False if using_array_manager else True + with tm.assert_produces_warning( + com.SettingWithCopyWarning, + raise_on_extra_warnings=raise_on_extra_warnings, + ): + subset.loc[:, "a"] = np.array([10, 11], dtype="int64") + + subset._mgr._verify_integrity() + expected = DataFrame( + {"a": [10, 11], "b": [5, 6], "c": np.array([8, 9], dtype=dtype)}, + index=range(1, 3), + ) + tm.assert_frame_equal(subset, expected) + if using_copy_on_write or using_array_manager: + # original parent dataframe is not modified (CoW) + tm.assert_frame_equal(df, df_orig) + else: + # original parent dataframe is actually updated + df_orig.loc[1:3, "a"] = np.array([10, 11], dtype="int64") + tm.assert_frame_equal(df, df_orig) + + +def test_subset_set_column_with_loc2(using_copy_on_write, using_array_manager): + # Case: setting a single column with loc on a viewing subset + # -> subset.loc[:, col] = value + # separate test for case of DataFrame of a single column -> takes a separate + # code path + df = DataFrame({"a": [1, 2, 3]}) + df_orig = df.copy() + subset = df[1:3] + + if using_copy_on_write: + subset.loc[:, "a"] = 0 + else: + with pd.option_context("chained_assignment", "warn"): + # The (i)loc[:, col] inplace deprecation gets triggered here, ignore those + # warnings and only assert the SettingWithCopyWarning + raise_on_extra_warnings = False if using_array_manager else True + with tm.assert_produces_warning( + com.SettingWithCopyWarning, + raise_on_extra_warnings=raise_on_extra_warnings, + ): + subset.loc[:, "a"] = 0 + + subset._mgr._verify_integrity() + expected = DataFrame({"a": [0, 0]}, index=range(1, 3)) + tm.assert_frame_equal(subset, expected) + if using_copy_on_write or using_array_manager: + # original parent dataframe is not modified (CoW) + tm.assert_frame_equal(df, df_orig) + else: + # original parent dataframe is actually updated + df_orig.loc[1:3, "a"] = 0 + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"] +) +def test_subset_set_columns(using_copy_on_write, dtype): + # Case: setting multiple columns on a viewing subset + # -> subset[[col1, col2]] = value + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)} + ) + df_orig = df.copy() + subset = df[1:3] + + if using_copy_on_write: + subset[["a", "c"]] = 0 + else: + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(com.SettingWithCopyWarning): + subset[["a", "c"]] = 0 + + subset._mgr._verify_integrity() + if using_copy_on_write: + # first and third column should certainly have no references anymore + assert all(subset._mgr._has_no_reference(i) for i in [0, 2]) + expected = DataFrame({"a": [0, 0], "b": [5, 6], "c": [0, 0]}, index=range(1, 3)) + tm.assert_frame_equal(subset, expected) + tm.assert_frame_equal(df, df_orig) + + +@pytest.mark.parametrize( + "indexer", + [slice("a", "b"), np.array([True, True, False]), ["a", "b"]], + ids=["slice", "mask", "array"], +) +def test_subset_set_with_column_indexer( + indexer, using_copy_on_write, using_array_manager +): + # Case: setting multiple columns with a column indexer on a viewing subset + # -> subset.loc[:, [col1, col2]] = value + df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3], "c": [4, 5, 6]}) + df_orig = df.copy() + subset = df[1:3] + + if using_copy_on_write: + subset.loc[:, indexer] = 0 + else: + with pd.option_context("chained_assignment", "warn"): + # The (i)loc[:, col] inplace deprecation gets triggered here, ignore those + # warnings and only assert the SettingWithCopyWarning + with tm.assert_produces_warning( + com.SettingWithCopyWarning, raise_on_extra_warnings=False + ): + subset.loc[:, indexer] = 0 + + subset._mgr._verify_integrity() + expected = DataFrame({"a": [0, 0], "b": [0.0, 0.0], "c": [5, 6]}, index=range(1, 3)) + # TODO full row slice .loc[:, idx] update inplace instead of overwrite? + expected["b"] = expected["b"].astype("int64") + tm.assert_frame_equal(subset, expected) + if using_copy_on_write or using_array_manager: + tm.assert_frame_equal(df, df_orig) + else: + # In the mixed case with BlockManager, only one of the two columns is + # mutated in the parent frame .. + df_orig.loc[1:2, ["a"]] = 0 + tm.assert_frame_equal(df, df_orig) + + +# TODO add more tests modifying the parent + + +# ----------------------------------------------------------------------------- +# Series -- Indexing operations taking subset + modifying the subset/parent + + +def test_series_getitem_slice(using_copy_on_write): + # Case: taking a slice of a Series + afterwards modifying the subset + s = Series([1, 2, 3], index=["a", "b", "c"]) + s_orig = s.copy() + + subset = s[:] + assert np.shares_memory(subset.values, s.values) + + subset.iloc[0] = 0 + + if using_copy_on_write: + assert not np.shares_memory(subset.values, s.values) + + expected = Series([0, 2, 3], index=["a", "b", "c"]) + tm.assert_series_equal(subset, expected) + + if using_copy_on_write: + # original parent series is not modified (CoW) + tm.assert_series_equal(s, s_orig) + else: + # original parent series is actually updated + assert s.iloc[0] == 0 + + +@pytest.mark.parametrize( + "indexer", + [slice(0, 2), np.array([True, True, False]), np.array([0, 1])], + ids=["slice", "mask", "array"], +) +def test_series_subset_set_with_indexer(indexer_si, indexer, using_copy_on_write): + # Case: setting values in a viewing Series with an indexer + s = Series([1, 2, 3], index=["a", "b", "c"]) + s_orig = s.copy() + subset = s[:] + + indexer_si(subset)[indexer] = 0 + expected = Series([0, 0, 3], index=["a", "b", "c"]) + tm.assert_series_equal(subset, expected) + + if using_copy_on_write: + tm.assert_series_equal(s, s_orig) + else: + tm.assert_series_equal(s, expected) + + +# ----------------------------------------------------------------------------- +# del operator + + +def test_del_frame(using_copy_on_write): + # Case: deleting a column with `del` on a viewing child dataframe should + # not modify parent + update the references + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + df2 = df[:] + + assert np.shares_memory(get_array(df, "a"), get_array(df2, "a")) + + del df2["b"] + + assert np.shares_memory(get_array(df, "a"), get_array(df2, "a")) + tm.assert_frame_equal(df, df_orig) + tm.assert_frame_equal(df2, df_orig[["a", "c"]]) + df2._mgr._verify_integrity() + + # TODO in theory modifying column "b" of the parent wouldn't need a CoW + # but the weakref is still alive and so we still perform CoW + + df2.loc[0, "a"] = 100 + if using_copy_on_write: + # modifying child after deleting a column still doesn't update parent + tm.assert_frame_equal(df, df_orig) + else: + assert df.loc[0, "a"] == 100 + + +def test_del_series(): + s = Series([1, 2, 3], index=["a", "b", "c"]) + s_orig = s.copy() + s2 = s[:] + + assert np.shares_memory(s.values, s2.values) + + del s2["a"] + + assert not np.shares_memory(s.values, s2.values) + tm.assert_series_equal(s, s_orig) + tm.assert_series_equal(s2, s_orig[["b", "c"]]) + + # modifying s2 doesn't need copy on write (due to `del`, s2 is backed by new array) + values = s2.values + s2.loc["b"] = 100 + assert values[0] == 100 + + +# ----------------------------------------------------------------------------- +# Accessing column as Series + + +def test_column_as_series(using_copy_on_write, using_array_manager): + # Case: selecting a single column now also uses Copy-on-Write + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + + s = df["a"] + + assert np.shares_memory(s.values, get_array(df, "a")) + + if using_copy_on_write or using_array_manager: + s[0] = 0 + else: + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(com.SettingWithCopyWarning): + s[0] = 0 + + expected = Series([0, 2, 3], name="a") + tm.assert_series_equal(s, expected) + if using_copy_on_write: + # assert not np.shares_memory(s.values, get_array(df, "a")) + tm.assert_frame_equal(df, df_orig) + # ensure cached series on getitem is not the changed series + tm.assert_series_equal(df["a"], df_orig["a"]) + else: + df_orig.iloc[0, 0] = 0 + tm.assert_frame_equal(df, df_orig) + + +def test_column_as_series_set_with_upcast(using_copy_on_write, using_array_manager): + # Case: selecting a single column now also uses Copy-on-Write -> when + # setting a value causes an upcast, we don't need to update the parent + # DataFrame through the cache mechanism + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + + s = df["a"] + if using_copy_on_write or using_array_manager: + s[0] = "foo" + else: + with pd.option_context("chained_assignment", "warn"): + with tm.assert_produces_warning(com.SettingWithCopyWarning): + s[0] = "foo" + + expected = Series(["foo", 2, 3], dtype=object, name="a") + tm.assert_series_equal(s, expected) + if using_copy_on_write: + tm.assert_frame_equal(df, df_orig) + # ensure cached series on getitem is not the changed series + tm.assert_series_equal(df["a"], df_orig["a"]) + else: + df_orig["a"] = expected + tm.assert_frame_equal(df, df_orig) + + +# TODO add tests for other indexing methods on the Series + + +def test_dataframe_add_column_from_series(): + # Case: adding a new column to a DataFrame from an existing column/series + # -> always already takes a copy on assignment + # (no change in behaviour here) + # TODO can we achieve the same behaviour with Copy-on-Write? + df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]}) + + s = Series([10, 11, 12]) + df["new"] = s + assert not np.shares_memory(get_array(df, "new"), s.values) + + # editing series -> doesn't modify column in frame + s[0] = 0 + expected = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3], "new": [10, 11, 12]}) + tm.assert_frame_equal(df, expected) + + # editing column in frame -> doesn't modify series + df.loc[2, "new"] = 100 + expected_s = Series([0, 11, 12]) + tm.assert_series_equal(s, expected_s) + + +# TODO add tests for constructors diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py new file mode 100644 index 0000000000000..1ed458e95b78e --- /dev/null +++ b/pandas/tests/copy_view/test_methods.py @@ -0,0 +1,128 @@ +import numpy as np + +from pandas import DataFrame +import pandas._testing as tm +from pandas.tests.copy_view.util import get_array + + +def test_copy(using_copy_on_write): + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_copy = df.copy() + + # the deep copy doesn't share memory + assert not np.shares_memory(get_array(df_copy, "a"), get_array(df, "a")) + if using_copy_on_write: + assert df_copy._mgr.refs is None + + # mutating copy doesn't mutate original + df_copy.iloc[0, 0] = 0 + assert df.iloc[0, 0] == 1 + + +def test_copy_shallow(using_copy_on_write): + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_copy = df.copy(deep=False) + + # the shallow copy still shares memory + assert np.shares_memory(get_array(df_copy, "a"), get_array(df, "a")) + if using_copy_on_write: + assert df_copy._mgr.refs is not None + + if using_copy_on_write: + # mutating shallow copy doesn't mutate original + df_copy.iloc[0, 0] = 0 + assert df.iloc[0, 0] == 1 + # mutating triggered a copy-on-write -> no longer shares memory + assert not np.shares_memory(get_array(df_copy, "a"), get_array(df, "a")) + # but still shares memory for the other columns/blocks + assert np.shares_memory(get_array(df_copy, "c"), get_array(df, "c")) + else: + # mutating shallow copy does mutate original + df_copy.iloc[0, 0] = 0 + assert df.iloc[0, 0] == 0 + # and still shares memory + assert np.shares_memory(get_array(df_copy, "a"), get_array(df, "a")) + + +# ----------------------------------------------------------------------------- +# DataFrame methods returning new DataFrame using shallow copy + + +def test_reset_index(using_copy_on_write): + # Case: resetting the index (i.e. adding a new column) + mutating the + # resulting dataframe + df = DataFrame( + {"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=[10, 11, 12] + ) + df_orig = df.copy() + df2 = df.reset_index() + df2._mgr._verify_integrity() + + if using_copy_on_write: + # still shares memory (df2 is a shallow copy) + assert np.shares_memory(get_array(df2, "b"), get_array(df, "b")) + assert np.shares_memory(get_array(df2, "c"), get_array(df, "c")) + # mutating df2 triggers a copy-on-write for that column / block + df2.iloc[0, 2] = 0 + assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b")) + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "c"), get_array(df, "c")) + tm.assert_frame_equal(df, df_orig) + + +def test_rename_columns(using_copy_on_write): + # Case: renaming columns returns a new dataframe + # + afterwards modifying the result + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + df2 = df.rename(columns=str.upper) + + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "A"), get_array(df, "a")) + df2.iloc[0, 0] = 0 + assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a")) + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "C"), get_array(df, "c")) + expected = DataFrame({"A": [0, 2, 3], "B": [4, 5, 6], "C": [0.1, 0.2, 0.3]}) + tm.assert_frame_equal(df2, expected) + tm.assert_frame_equal(df, df_orig) + + +def test_rename_columns_modify_parent(using_copy_on_write): + # Case: renaming columns returns a new dataframe + # + afterwards modifying the original (parent) dataframe + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df2 = df.rename(columns=str.upper) + df2_orig = df2.copy() + + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "A"), get_array(df, "a")) + else: + assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a")) + df.iloc[0, 0] = 0 + assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a")) + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "C"), get_array(df, "c")) + expected = DataFrame({"a": [0, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + tm.assert_frame_equal(df, expected) + tm.assert_frame_equal(df2, df2_orig) + + +def test_reindex_columns(using_copy_on_write): + # Case: reindexing the column returns a new dataframe + # + afterwards modifying the result + df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}) + df_orig = df.copy() + df2 = df.reindex(columns=["a", "c"]) + + if using_copy_on_write: + # still shares memory (df2 is a shallow copy) + assert np.shares_memory(get_array(df2, "a"), get_array(df, "a")) + else: + assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a")) + # mutating df2 triggers a copy-on-write for that column + df2.iloc[0, 0] = 0 + assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a")) + if using_copy_on_write: + assert np.shares_memory(get_array(df2, "c"), get_array(df, "c")) + tm.assert_frame_equal(df, df_orig) diff --git a/pandas/tests/copy_view/util.py b/pandas/tests/copy_view/util.py new file mode 100644 index 0000000000000..9e358c7eec749 --- /dev/null +++ b/pandas/tests/copy_view/util.py @@ -0,0 +1,11 @@ +def get_array(df, col): + """ + Helper method to get array for a DataFrame column. + + Equivalent of df[col].values, but without going through normal getitem, + which triggers tracking references / CoW (and we might be testing that + this is done by some other operation). + """ + icol = df.columns.get_loc(col) + assert isinstance(icol, int) + return df._get_column_array(icol)