BUG: 2D ndarray of dtype 'object' is always copied upon construction

[irgolic]

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

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

import numpy as np                             
import pandas as pd    
                                                                                                                                                                                                                                                
a = np.array(['a', 'b'], dtype='object')                                                                                                                                                                                                                                                                                                                                                    
df = pd.DataFrame(a)                                                                                                                                                                                       

assert np.shares_memory(df.values, a)  # True         
                                                                                                                                                                      
b = np.array([['a', 'b'], 
              ['c', 'd']], dtype='object')                                                                                                                                                                                 
df2 = pd.DataFrame(b)                                                                                                                                                                                     

assert np.shares_memory(df2.values, b)  # False

Problem description

This issue addresses the TODO in pandas.core.internals.construction.py, line 250 on master at time of writing. This was introduced by #26825. It's quite annoying, I'm trying to use DataFrame as an interface to access my dtype object numpy array, but I can't without copying it in first.

Expected Output

Exit code 0.

Output of pd.show_versions()

INSTALLED VERSIONS

commit : b5958ee
python : 3.6.10.final.0
python-bits : 64
OS : Darwin
OS-release : 19.6.0
Version : Darwin Kernel Version 19.6.0: Mon Aug 31 22:12:52 PDT 2020; root:xnu-6153.141.2~1/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 1.1.5
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.1.3
Cython : 0.29.14
pytest : 5.3.5
hypothesis : 5.4.1
sphinx : 2.3.1
blosc : None
feather : None
xlsxwriter : 1.2.8
lxml.etree : 4.5.0
html5lib : 1.0.1
pymysql : None
psycopg2 : None
jinja2 : 2.11.1
IPython : 7.12.0
pandas_datareader: None
bs4 : 4.8.2
bottleneck : 1.3.1
fsspec : 0.6.2
fastparquet : None
gcsfs : None
matplotlib : 3.2.1
numexpr : 2.7.1
odfpy : None
openpyxl : 3.0.3
pandas_gbq : None
pyarrow : None
pytables : None
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : 1.3.13
tables : 3.6.1
tabulate : None
xarray : None
xlrd : 1.2.0
xlwt : 1.2.0
numba : 0.48.0