BUG: the behavior of "date_range" function with "periods & inclusive" arguments

[idanhazan]

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

pd.date_range(start='2020-06-01', periods=4, inclusive='both')
# DatetimeIndex(['2020-06-01', '2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')

pd.date_range(start='2020-06-01', periods=4, inclusive='neither')
# Output:
# DatetimeIndex(['2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')
# Expected:
# DatetimeIndex(['2020-06-02', '2020-06-03'], dtype='datetime64[ns]', freq='D')

pd.date_range(start='2020-06-01', periods=4, inclusive='left')
# Output:
# DatetimeIndex(['2020-06-01', '2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')
# Expected:
# DatetimeIndex(['2020-06-01', '2020-06-02', '2020-06-03'], dtype='datetime64[ns]', freq='D')

pd.date_range(start='2020-06-01', periods=4, inclusive='right')
# DatetimeIndex(['2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')

Issue Description

First of all, I have no idea if it actually a bug, maybe it not understood for me.

How do I think the function should bring the output:

Calculate with inclusive=True and then filter out left/right/both at the edges.

Expected Behavior

pd.date_range(start='2020-06-01', periods=4, inclusive='neither')

# Output:
DatetimeIndex(['2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')

# Expected:
DatetimeIndex(['2020-06-02', '2020-06-03'], dtype='datetime64[ns]', freq='D')

pd.date_range(start='2020-06-01', periods=4, inclusive='left')

# Output:
DatetimeIndex(['2020-06-01', '2020-06-02', '2020-06-03', '2020-06-04'], dtype='datetime64[ns]', freq='D')

# Expected:
DatetimeIndex(['2020-06-01', '2020-06-02', '2020-06-03'], dtype='datetime64[ns]', freq='D')

Installed Versions

INSTALLED VERSIONS

commit : 06d2301
python : 3.9.10.final.0
python-bits : 64
OS : Linux
OS-release : 5.13.0-30-generic
Version : #33-Ubuntu SMP Fri Feb 4 17:03:31 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_IL
LOCALE : en_IL.UTF-8

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 : None
hypothesis : None
sphinx : 4.4.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.8.0
html5lib : None
pymysql : None
psycopg2 : 2.9.3
jinja2 : 3.0.3
IPython : 7.32.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
fsspec : 2022.02.0
gcsfs : None
matplotlib : 3.5.1
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : 2022.02.0
scipy : 1.8.0
sqlalchemy : 1.4.31
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None

[attack68]

I agree with you that this does not appear consistent, even with my comment below.

Interestingly, it rather throws up an odd nomenclature item. Is a period defined as that between two timepoints or as a single time point, i.e. is [time1, time2, time3] two periods or three? It seems that pandas has adopted the three periods definition and as such that probably wont be changed but the inclusive arg should work properly I think. This might break a lot of tests though.