TypeError: copy() takes no keyword arguments

[BayerSe]

Code Sample, a copy-pastable example if possible

import pandas as pd

df = pd.DataFrame(['A', 'A', 'B', 'B'], columns=['grps'])
df.groupby('grps').apply(lambda x: x.index.to_list())

Traceback (most recent call last):
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/groupby.py", line 735, in apply
    result = self._python_apply_general(f)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/groupby.py", line 751, in _python_apply_general
    keys, values, mutated = self.grouper.apply(f, self._selected_obj, self.axis)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/ops.py", line 171, in apply
    result_values, mutated = splitter.fast_apply(f, group_keys)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/ops.py", line 925, in fast_apply
    return libreduction.apply_frame_axis0(sdata, f, names, starts, ends)
  File "pandas/_libs/reduction.pyx", line 505, in pandas._libs.reduction.apply_frame_axis0
TypeError: copy() takes no keyword arguments
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3319, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-2-a3e576516eed>", line 4, in <module>
    df.groupby('grps').apply(lambda x: x.index.to_list())
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/groupby.py", line 746, in apply
    return self._python_apply_general(f)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/groupby.py", line 751, in _python_apply_general
    keys, values, mutated = self.grouper.apply(f, self._selected_obj, self.axis)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/ops.py", line 171, in apply
    result_values, mutated = splitter.fast_apply(f, group_keys)
  File "/home/bay2rng/miniconda3/envs/p356_rtp_production_scheduling/lib/python3.7/site-packages/pandas/core/groupby/ops.py", line 925, in fast_apply
    return libreduction.apply_frame_axis0(sdata, f, names, starts, ends)
  File "pandas/_libs/reduction.pyx", line 505, in pandas._libs.reduction.apply_frame_axis0
TypeError: copy() takes no keyword arguments

Problem description

This snippet is working well on version 0.25.3. It breaks in version 1.0.0.

Expected Output

A    [0, 1]
B    [2, 3]
dtype: object

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.7.6.final.0
python-bits : 64
OS : Linux
OS-release : 4.15.0-72-generic
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 1.0.0
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 45.1.0.post20200127
Cython : None
pytest : 5.3.2
hypothesis : None
sphinx : 2.3.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.10.3
IPython : 7.11.1
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
gcsfs : None
lxml.etree : None
matplotlib : 3.1.2
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 0.15.1
pytables : None
pytest : 5.3.2
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : 1.3.13
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None
numba : None

[jorisvandenbossche]

@BayerSe thanks for the report!

cc @jbrockmendel

[getsanjeevdubey]

@BayerSe @jorisvandenbossche I get the same error in 0.25.3
Not on this above mentioned dataframe, but on my own data.

[MarcoGorelli]

When the code reaches "pandas/_libs/reduction.pyx", line 505:

                    piece = piece.copy(deep="all")

then piece is

<class 'list'>
[0, 1]

Is the fix here to use copy.deepcopy if piece is a list?

[jbrockmendel]

I think this is caused by #28662, cc @dsaxton.

[getsanjeevdubey]

@jbrockmendel Any immediate solutions, is it fixed in other versions like 0.25.1

[dsaxton]

I think this is caused by #28662, cc @dsaxton.

@jbrockmendel I think you're right. The implicit assumption there was apparently that piece would be a pandas object, but as the list example shows that doesn't have to be true.

[jreback]

use a try/except around the .copy(..)

will fix this (and use deepcopy in the except

[MarcoGorelli]

and use deepcopy in the except

Tried that, but then pandas/tests/plotting/test_groupby.py::TestDataFrameGroupByPlots.test_plot_kwargs fails.

Also, I wasn't able to reproduce an example where using copy (instead of deepcopy) doesn't give the output I was expecting