BUG: DataFrame.replace with dict doesn't work when value=None

[zeromh]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd
df = pd.DataFrame(dict(a=[1,2,3],
                      b=[1,2,3]))
df.replace({1:5}, value=None) # does not replace values at all
df.replace({1:5}) # correctly replaces 1s with 5s

Issue Description

The documentation for DataFrame.replace says, for the to_replace argument, that:

Dicts can be used to specify different replacement values for different existing values. For example, {'a': 'b', 'y': 'z'} replaces the value ‘a’ with ‘b’ and ‘y’ with ‘z’. To use a dict in this way the value parameter should be None.

However, specifying value=None results in no replacement taking place. If I don't specify value at all, it works.

Expected Behavior

I expect (based on the docs) that specifying value=None will allow using a dictionary for replacement.

Installed Versions

INSTALLED VERSIONS

commit : 06d2301
python : 3.8.13.final.0
python-bits : 64
OS : Linux
OS-release : 5.10.93-87.444.amzn2.x86_64
Version : #1 SMP Thu Jan 20 22:50:50 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.4.1
numpy : 1.22.3
pytz : 2022.1
dateutil : 2.8.2
pip : 21.2.4
setuptools : 58.0.4
Cython : None
pytest : 7.1.1
hypothesis : None
sphinx : 4.5.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.1
IPython : 8.1.1
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : 0.8.1
fsspec : 2022.3.0
gcsfs : None
matplotlib : 3.5.1
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 3.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.8.0
sqlalchemy : None
tables : None
tabulate : 0.8.9
xarray : None
xlrd : None
xlwt : None
zstandard : None

[Kyrpel]

take

[simonjayhawkins]

Thanks @zeromh for the report

The documentation for DataFrame.replace says, for the to_replace argument, that:

This does look like a documentation error. probably should be To use a dict in this way the value parameter should be None. -> To use a dict in this way, the optional value parameter should not be given.

since df.replace({1: 5}, value=10) does not replace either, it is not limited to None

also note that if you put a dict in the DataFrame then it still does not work...

df = pd.DataFrame(dict(a=[{1: 5}, 2, 3], b=[1, 2, 3]), dtype=object)
df.replace({1: 5}, value=10)

because this is reserved for a special case where the values to replace are restricted to certain columns

so this does work

df = pd.DataFrame({1: [5, 2, 3], "b": [1, 2, 3]})
df.replace({1: 5}, value=10)

so specifying a mapping for to_replace and also specifying a value for the replacement of the narrowed columns is allowed through the validation in the example in the OP.

This gets more tricky with

df = pd.DataFrame(dict(a=[{1: 5}, 2, 3], b=[1, 2, 3]), dtype=object)
df.replace({"a": {1: 5}}, value=10)

which is then interpreted as a nested replacement dictionary so does not necessarily give the result expected and raises ValueError: Series.replace cannot use dict-like to_replace and non-None value

and if you have a None replacement value where you might expected the result to be cast to object dtype, say

df = pd.DataFrame(dict(a=[1, 2, 3], b=[1, 2, 3]))
df.replace({"a": 1}, value=None)

you get a RecursionError!

whereas

df = pd.DataFrame(dict(a=[1, 2, 3], b=[1, 2, 3]))
df.replace({"a": {1: None}})

does work. The docs for the nested dictionary case also probably need updating too The value parameter should be None to use a nested dict in this way. -> The optional value parameter should not be specified to use a nested dict in this way.

[ivan-afonichkin]

take

[simonjayhawkins]

xref #46004 for related issue for Series.

[nkathy]

take

[stanleycai95]

take