BUG: DatetimeIndex.copy() not making deep copy #49356
Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
i1 = pd.date_range("2022", freq="D", periods=10)
i2 = i1.copy() # COPY
print(i1 is i2) # False
print(id(i1), id(i2)) # 2151608624624 2151619591232
print(i1.freq) # <Day>
print(i2.freq) # <Day>
i1.freq = None
print(i1 is i2) # False
print(id(i1), id(i2)) # 2151608624624 2151619591232
print(i1.freq) # None
print(i2.freq) # None (!!)Issue Description
See the final line. The frequency of i2 has been changed as well, even though it is a distinct object from i1.
Excuse me if this is expected.
Expected Behavior
The attributes of i2 should not change when they are changed in i1 only.
Installed Versions
Details
INSTALLED VERSIONS ------------------ commit : 91111fd python : 3.8.13.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19045 machine : AMD64 processor : Intel64 Family 6 Model 165 Stepping 2, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : de_DE.cp1252pandas : 1.5.1
numpy : 1.23.4
pytz : 2022.5
dateutil : 2.8.2
setuptools : 61.2.0
pip : 21.2.2
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 : 3.1.2
IPython : 8.3.0
pandas_datareader: None
bs4 : None
bottleneck : None
brotli :
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.6.1
numba : None
numexpr : None
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : None
snappy : None
sqlalchemy : 1.4.32
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None
tzdata : None