test_constructors.py

import numpy as np
import pytest

import pandas as pd
from pandas import (
    DataFrame,
    DatetimeIndex,
    Index,
    Period,
    PeriodIndex,
    Series,
    Timedelta,
    TimedeltaIndex,
    Timestamp,
)
import pandas._testing as tm
from pandas.tests.copy_view.util import get_array

# -----------------------------------------------------------------------------
# Copy/view behaviour for Series / DataFrame constructors


@pytest.mark.parametrize("dtype", [None, "int64"])
def test_series_from_series(dtype, using_copy_on_write):
    # Case: constructing a Series from another Series object follows CoW rules:
    # a new object is returned and thus mutations are not propagated
    ser = Series([1, 2, 3], name="name")

    # default is copy=False -> new Series is a shallow copy / view of original
    result = Series(ser, dtype=dtype)

    # the shallow copy still shares memory
    assert np.shares_memory(get_array(ser), get_array(result))

    if using_copy_on_write:
        assert result._mgr.blocks[0].refs.has_reference()

    if using_copy_on_write:
        # mutating new series copy doesn't mutate original
        result.iloc[0] = 0
        assert ser.iloc[0] == 1
        # mutating triggered a copy-on-write -> no longer shares memory
        assert not np.shares_memory(get_array(ser), get_array(result))
    else:
        # mutating shallow copy does mutate original
        result.iloc[0] = 0
        assert ser.iloc[0] == 0
        # and still shares memory
        assert np.shares_memory(get_array(ser), get_array(result))

    # the same when modifying the parent
    result = Series(ser, dtype=dtype)

    if using_copy_on_write:
        # mutating original doesn't mutate new series
        ser.iloc[0] = 0
        assert result.iloc[0] == 1
    else:
        # mutating original does mutate shallow copy
        ser.iloc[0] = 0
        assert result.iloc[0] == 0


def test_series_from_series_with_reindex(using_copy_on_write):
    # Case: constructing a Series from another Series with specifying an index
    # that potentially requires a reindex of the values
    ser = Series([1, 2, 3], name="name")

    # passing an index that doesn't actually require a reindex of the values
    # -> without CoW we get an actual mutating view
    for index in [
        ser.index,
        ser.index.copy(),
        list(ser.index),
        ser.index.rename("idx"),
    ]:
        result = Series(ser, index=index)
        assert np.shares_memory(ser.values, result.values)
        result.iloc[0] = 0
        if using_copy_on_write:
            assert ser.iloc[0] == 1
        else:
            assert ser.iloc[0] == 0

    # ensure that if an actual reindex is needed, we don't have any refs
    # (mutating the result wouldn't trigger CoW)
    result = Series(ser, index=[0, 1, 2, 3])
    assert not np.shares_memory(ser.values, result.values)
    if using_copy_on_write:
        assert not result._mgr.blocks[0].refs.has_reference()


@pytest.mark.parametrize("fastpath", [False, True])
@pytest.mark.parametrize("dtype", [None, "int64"])
@pytest.mark.parametrize("idx", [None, pd.RangeIndex(start=0, stop=3, step=1)])
@pytest.mark.parametrize(
    "arr", [np.array([1, 2, 3], dtype="int64"), pd.array([1, 2, 3], dtype="Int64")]
)
def test_series_from_array(using_copy_on_write, idx, dtype, fastpath, arr):
    if idx is None or dtype is not None:
        fastpath = False
    ser = Series(arr, dtype=dtype, index=idx, fastpath=fastpath)
    ser_orig = ser.copy()
    data = getattr(arr, "_data", arr)
    if using_copy_on_write:
        assert not np.shares_memory(get_array(ser), data)
    else:
        assert np.shares_memory(get_array(ser), data)

    arr[0] = 100
    if using_copy_on_write:
        tm.assert_series_equal(ser, ser_orig)
    else:
        expected = Series([100, 2, 3], dtype=dtype if dtype is not None else arr.dtype)
        tm.assert_series_equal(ser, expected)


@pytest.mark.parametrize("copy", [True, False, None])
def test_series_from_array_different_dtype(using_copy_on_write, copy):
    arr = np.array([1, 2, 3], dtype="int64")
    ser = Series(arr, dtype="int32", copy=copy)
    assert not np.shares_memory(get_array(ser), arr)


@pytest.mark.parametrize(
    "idx",
    [
        Index([1, 2]),
        DatetimeIndex([Timestamp("2019-12-31"), Timestamp("2020-12-31")]),
        PeriodIndex([Period("2019-12-31"), Period("2020-12-31")]),
        TimedeltaIndex([Timedelta("1 days"), Timedelta("2 days")]),
    ],
)
def test_series_from_index(using_copy_on_write, idx):
    ser = Series(idx)
    expected = idx.copy(deep=True)
    if using_copy_on_write:
        assert np.shares_memory(get_array(ser), get_array(idx))
        assert not ser._mgr._has_no_reference(0)
    else:
        assert not np.shares_memory(get_array(ser), get_array(idx))
    ser.iloc[0] = ser.iloc[1]
    tm.assert_index_equal(idx, expected)


def test_series_from_index_different_dtypes(using_copy_on_write):
    idx = Index([1, 2, 3], dtype="int64")
    ser = Series(idx, dtype="int32")
    assert not np.shares_memory(get_array(ser), get_array(idx))
    if using_copy_on_write:
        assert ser._mgr._has_no_reference(0)


@pytest.mark.parametrize("fastpath", [False, True])
@pytest.mark.parametrize("dtype", [None, "int64"])
@pytest.mark.parametrize("idx", [None, pd.RangeIndex(start=0, stop=3, step=1)])
def test_series_from_block_manager(using_copy_on_write, idx, dtype, fastpath):
    ser = Series([1, 2, 3], dtype="int64")
    ser_orig = ser.copy()
    ser2 = Series(ser._mgr, dtype=dtype, fastpath=fastpath, index=idx)
    assert np.shares_memory(get_array(ser), get_array(ser2))
    if using_copy_on_write:
        assert not ser2._mgr._has_no_reference(0)

    ser2.iloc[0] = 100
    if using_copy_on_write:
        tm.assert_series_equal(ser, ser_orig)
    else:
        expected = Series([100, 2, 3])
        tm.assert_series_equal(ser, expected)


def test_series_from_block_manager_different_dtype(using_copy_on_write):
    ser = Series([1, 2, 3], dtype="int64")
    ser2 = Series(ser._mgr, dtype="int32")
    assert not np.shares_memory(get_array(ser), get_array(ser2))
    if using_copy_on_write:
        assert ser2._mgr._has_no_reference(0)


@pytest.mark.parametrize("func", [lambda x: x, lambda x: x._mgr])
@pytest.mark.parametrize("columns", [None, ["a"]])
def test_dataframe_constructor_mgr_or_df(using_copy_on_write, columns, func):
    df = DataFrame({"a": [1, 2, 3]})
    df_orig = df.copy()

    new_df = DataFrame(func(df))

    assert np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
    new_df.iloc[0] = 100

    if using_copy_on_write:
        assert not np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
        tm.assert_frame_equal(df, df_orig)
    else:
        assert np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
        tm.assert_frame_equal(df, new_df)


@pytest.mark.parametrize("dtype", [None, "int64", "Int64"])
@pytest.mark.parametrize("index", [None, [0, 1, 2]])
@pytest.mark.parametrize("columns", [None, ["a", "b"], ["a", "b", "c"]])
def test_dataframe_from_dict_of_series(
    request, using_copy_on_write, columns, index, dtype
):
    # Case: constructing a DataFrame from Series objects with copy=False
    # has to do a lazy following CoW rules
    # (the default for DataFrame(dict) is still to copy to ensure consolidation)
    s1 = Series([1, 2, 3])
    s2 = Series([4, 5, 6])
    s1_orig = s1.copy()
    expected = DataFrame(
        {"a": [1, 2, 3], "b": [4, 5, 6]}, index=index, columns=columns, dtype=dtype
    )

    result = DataFrame(
        {"a": s1, "b": s2}, index=index, columns=columns, dtype=dtype, copy=False
    )

    # the shallow copy still shares memory
    assert np.shares_memory(get_array(result, "a"), get_array(s1))

    # mutating the new dataframe doesn't mutate original
    result.iloc[0, 0] = 10
    if using_copy_on_write:
        assert not np.shares_memory(get_array(result, "a"), get_array(s1))
        tm.assert_series_equal(s1, s1_orig)
    else:
        assert s1.iloc[0] == 10

    # the same when modifying the parent series
    s1 = Series([1, 2, 3])
    s2 = Series([4, 5, 6])
    result = DataFrame(
        {"a": s1, "b": s2}, index=index, columns=columns, dtype=dtype, copy=False
    )
    s1.iloc[0] = 10
    if using_copy_on_write:
        assert not np.shares_memory(get_array(result, "a"), get_array(s1))
        tm.assert_frame_equal(result, expected)
    else:
        assert result.iloc[0, 0] == 10


@pytest.mark.parametrize("dtype", [None, "int64"])
def test_dataframe_from_dict_of_series_with_reindex(dtype):
    # Case: constructing a DataFrame from Series objects with copy=False
    # and passing an index that requires an actual (no-view) reindex -> need
    # to ensure the result doesn't have refs set up to unnecessarily trigger
    # a copy on write
    s1 = Series([1, 2, 3])
    s2 = Series([4, 5, 6])
    df = DataFrame({"a": s1, "b": s2}, index=[1, 2, 3], dtype=dtype, copy=False)

    # df should own its memory, so mutating shouldn't trigger a copy
    arr_before = get_array(df, "a")
    assert not np.shares_memory(arr_before, get_array(s1))
    df.iloc[0, 0] = 100
    arr_after = get_array(df, "a")
    assert np.shares_memory(arr_before, arr_after)


@pytest.mark.parametrize("cons", [Series, Index])
@pytest.mark.parametrize(
    "data, dtype", [([1, 2], None), ([1, 2], "int64"), (["a", "b"], None)]
)
def test_dataframe_from_series_or_index(using_copy_on_write, data, dtype, cons):
    obj = cons(data, dtype=dtype)
    obj_orig = obj.copy()
    df = DataFrame(obj, dtype=dtype)
    assert np.shares_memory(get_array(obj), get_array(df, 0))
    if using_copy_on_write:
        assert not df._mgr._has_no_reference(0)

    df.iloc[0, 0] = data[-1]
    if using_copy_on_write:
        tm.assert_equal(obj, obj_orig)


@pytest.mark.parametrize("cons", [Series, Index])
def test_dataframe_from_series_or_index_different_dtype(using_copy_on_write, cons):
    obj = cons([1, 2], dtype="int64")
    df = DataFrame(obj, dtype="int32")
    assert not np.shares_memory(get_array(obj), get_array(df, 0))
    if using_copy_on_write:
        assert df._mgr._has_no_reference(0)


def test_dataframe_from_series_infer_datetime(using_copy_on_write):
    ser = Series([Timestamp("2019-12-31"), Timestamp("2020-12-31")], dtype=object)
    df = DataFrame(ser)
    assert not np.shares_memory(get_array(ser), get_array(df, 0))
    if using_copy_on_write:
        assert df._mgr._has_no_reference(0)


@pytest.mark.parametrize("index", [None, [0, 1, 2]])
def test_dataframe_from_dict_of_series_with_dtype(index):
    # Variant of above, but now passing a dtype that causes a copy
    # -> need to ensure the result doesn't have refs set up to unnecessarily
    # trigger a copy on write
    s1 = Series([1.0, 2.0, 3.0])
    s2 = Series([4, 5, 6])
    df = DataFrame({"a": s1, "b": s2}, index=index, dtype="int64", copy=False)

    # df should own its memory, so mutating shouldn't trigger a copy
    arr_before = get_array(df, "a")
    assert not np.shares_memory(arr_before, get_array(s1))
    df.iloc[0, 0] = 100
    arr_after = get_array(df, "a")
    assert np.shares_memory(arr_before, arr_after)


@pytest.mark.parametrize("copy", [False, None, True])
def test_frame_from_numpy_array(using_copy_on_write, copy, using_array_manager):
    arr = np.array([[1, 2], [3, 4]])
    df = DataFrame(arr, copy=copy)

    if (
        using_copy_on_write
        and copy is not False
        or copy is True
        or (using_array_manager and copy is None)
    ):
        assert not np.shares_memory(get_array(df, 0), arr)
    else:
        assert np.shares_memory(get_array(df, 0), arr)


def test_dataframe_from_records_with_dataframe(using_copy_on_write):
    df = DataFrame({"a": [1, 2, 3]})
    df_orig = df.copy()
    df2 = DataFrame.from_records(df)
    if using_copy_on_write:
        assert not df._mgr._has_no_reference(0)
    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
    df2.iloc[0, 0] = 100
    if using_copy_on_write:
        tm.assert_frame_equal(df, df_orig)
    else:
        tm.assert_frame_equal(df, df2)