test_chained_assignment_deprecation.py

import numpy as np
import pytest

from pandas.errors import ChainedAssignmentError

from pandas import DataFrame
import pandas._testing as tm


def test_methods_iloc_warn(using_copy_on_write):
    if not using_copy_on_write:
        df = DataFrame({"a": [1, 2, 3], "b": 1})
        with tm.assert_cow_warning(match="A value"):
            df.iloc[:, 0].replace(1, 5, inplace=True)

        with tm.assert_cow_warning(match="A value"):
            df.iloc[:, 0].fillna(1, inplace=True)

        with tm.assert_cow_warning(match="A value"):
            df.iloc[:, 0].interpolate(inplace=True)

        with tm.assert_cow_warning(match="A value"):
            df.iloc[:, 0].ffill(inplace=True)

        with tm.assert_cow_warning(match="A value"):
            df.iloc[:, 0].bfill(inplace=True)


@pytest.mark.parametrize(
    "func, args",
    [
        ("replace", (1, 5)),
        ("fillna", (1,)),
        ("interpolate", ()),
        ("bfill", ()),
        ("ffill", ()),
    ],
)
def test_methods_iloc_getitem_item_cache(func, args, using_copy_on_write):
    df = DataFrame({"a": [1, 2, 3], "b": 1})
    ser = df.iloc[:, 0]
    # TODO(CoW-warn) should warn about updating a view
    getattr(ser, func)(*args, inplace=True)

    # parent that holds item_cache is dead, so don't increase ref count
    ser = df.copy()["a"]
    getattr(ser, func)(*args, inplace=True)

    df = df.copy()

    df["a"]  # populate the item_cache
    ser = df.iloc[:, 0]  # iloc creates a new object
    ser.fillna(0, inplace=True)

    df["a"]  # populate the item_cache
    ser = df["a"]
    ser.fillna(0, inplace=True)

    df = df.copy()
    df["a"]  # populate the item_cache
    if using_copy_on_write:
        with tm.raises_chained_assignment_error():
            df["a"].fillna(0, inplace=True)
    else:
        with tm.assert_cow_warning(match="A value"):
            df["a"].fillna(0, inplace=True)


# TODO(CoW-warn) expand the cases
@pytest.mark.parametrize(
    "indexer", [0, [0, 1], slice(0, 2), np.array([True, False, True])]
)
def test_series_setitem(indexer, using_copy_on_write, warn_copy_on_write):
    # ensure we only get a single warning for those typical cases of chained
    # assignment
    df = DataFrame({"a": [1, 2, 3], "b": 1})

    # using custom check instead of tm.assert_produces_warning because that doesn't
    # fail if multiple warnings are raised
    with pytest.warns() as record:
        df["a"][indexer] = 0
    assert len(record) == 1
    if using_copy_on_write:
        assert record[0].category == ChainedAssignmentError
    else:
        assert record[0].category == FutureWarning
        assert "ChainedAssignmentError" in record[0].message.args[0]