test_chaining_and_caching.py

import numpy as np
import pytest

import pandas.util._test_decorators as td

from pandas import (
    DataFrame,
    MultiIndex,
    Series,
)
import pandas._testing as tm
import pandas.core.common as com


def test_detect_chained_assignment():
    # Inplace ops, originally from:
    # https://stackoverflow.com/questions/20508968/series-fillna-in-a-multiindex-dataframe-does-not-fill-is-this-a-bug
    a = [12, 23]
    b = [123, None]
    c = [1234, 2345]
    d = [12345, 23456]
    tuples = [("eyes", "left"), ("eyes", "right"), ("ears", "left"), ("ears", "right")]
    events = {
        ("eyes", "left"): a,
        ("eyes", "right"): b,
        ("ears", "left"): c,
        ("ears", "right"): d,
    }
    multiind = MultiIndex.from_tuples(tuples, names=["part", "side"])
    zed = DataFrame(events, index=["a", "b"], columns=multiind)

    msg = "A value is trying to be set on a copy of a slice from a DataFrame"
    with pytest.raises(com.SettingWithCopyError, match=msg):
        zed["eyes"]["right"].fillna(value=555, inplace=True)


@td.skip_array_manager_invalid_test  # with ArrayManager df.loc[0] is not a view
def test_cache_updating():
    # 5216
    # make sure that we don't try to set a dead cache
    a = np.random.rand(10, 3)
    df = DataFrame(a, columns=["x", "y", "z"])
    tuples = [(i, j) for i in range(5) for j in range(2)]
    index = MultiIndex.from_tuples(tuples)
    df.index = index

    # setting via chained assignment
    # but actually works, since everything is a view
    df.loc[0]["z"].iloc[0] = 1.0
    result = df.loc[(0, 0), "z"]
    assert result == 1

    # correct setting
    df.loc[(0, 0), "z"] = 2
    result = df.loc[(0, 0), "z"]
    assert result == 2


@pytest.mark.arm_slow
def test_indexer_caching():
    # GH5727
    # make sure that indexers are in the _internal_names_set
    n = 1000001
    arrays = (range(n), range(n))
    index = MultiIndex.from_tuples(zip(*arrays))
    s = Series(np.zeros(n), index=index)
    str(s)

    # setitem
    expected = Series(np.ones(n), index=index)
    s = Series(np.zeros(n), index=index)
    s[s == 0] = 1
    tm.assert_series_equal(s, expected)