BUG: DataFrame.__setitem__: ValueError: Expected a 1D array, got an array with shape (256, 2)

[anmyachev]

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
import numpy as np

df = pd.DataFrame(np.zeros((256, 10)))
array_2d = np.zeros((256, 2))
df["col33"] = array_2d  # failed, see the exception below
df[0] = array_2d  # works, the case where column name already exist in `df`

# Note: the same behavior is observed for `loc` function

Issue Description

Inconsistent behavior for cases where the column name is already used in the dataframe and when not.

Exception:

Traceback (most recent call last):
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\frame.py", line 3799, in _set_item_mgr
    loc = self._info_axis.get_loc(key)
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\indexes\range.py", line 389, in get_loc
    raise KeyError(key)
KeyError: 'col33'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\frame.py", line 3655, in __setitem__
    self._set_item(key, value)
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\frame.py", line 3845, in _set_item
    self._set_item_mgr(key, value)
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\frame.py", line 3802, in _set_item_mgr
    self._mgr.insert(len(self._info_axis), key, value)
  File "C:\Users\amyachev\Miniconda3\envs\modin\lib\site-packages\pandas\core\internals\managers.py", line 1235, in insert
    raise ValueError(
ValueError: Expected a 1D array, got an array with shape (256, 2)

Expected Behavior

Same behavior for both cases.

Installed Versions

INSTALLED VERSIONS

commit : 06d2301
python : 3.8.12.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19044
machine : AMD64
processor : Intel64 Family 6 Model 142 Stepping 12, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252

pandas : 1.4.1
numpy : 1.22.2
pytz : 2021.3
dateutil : 2.8.2
pip : 22.0.3
setuptools : 59.8.0
Cython : None
pytest : 7.0.0
hypothesis : None
sphinx : 4.4.0
blosc : None
feather : 0.4.1
xlsxwriter : None
lxml.etree : 4.7.1
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.0.1
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
fsspec : 2022.01.0
gcsfs : None
matplotlib : 3.2.2
numba : None
numexpr : 2.7.3
odfpy : None
openpyxl : 3.0.9
pandas_gbq : 0.17.0
pyarrow : 6.0.1
pyreadstat : None
pyxlsb : None
s3fs : 2022.01.0
scipy : 1.8.0
sqlalchemy : 1.4.31
tables : 3.7.0
tabulate : None
xarray : 0.21.1
xlrd : 2.0.1
xlwt : None
zstandard : None

[phofl]

Added this to #46544