BUG: Empty dataframe created with Index, not RangeIndex · Issue #40077 · pandas-dev/pandas (original) (raw)

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Code Sample, a copy-pastable example

Your code here

import pandas as pd df = pd.DataFrame(columns=['a', 'b']) print(df.index) Index([], dtype='object')

df2 = df.append(df, ignore_index=True) print(df2.index) RangeIndex(start=0, stop=0, step=1)

pd.testing.assert_frame_equal(df, df2) Traceback (most recent call last): File "", line 1, in File "/home/stefan/miniconda3/envs/pandas/lib/python3.9/site-packages/pandas/_testing.py", line 1657, in assert_frame_equal assert_index_equal( File "/home/stefan/miniconda3/envs/pandas/lib/python3.9/site-packages/pandas/_testing.py", line 773, in assert_index_equal _check_types(left, right, obj=obj) File "/home/stefan/miniconda3/envs/pandas/lib/python3.9/site-packages/pandas/_testing.py", line 740, in _check_types assert_class_equal(left, right, exact=exact, obj=obj) File "/home/stefan/miniconda3/envs/pandas/lib/python3.9/site-packages/pandas/_testing.py", line 868, in assert_class_equal raise_assert_detail(obj, msg, repr_class(left), repr_class(right)) File "/home/stefan/miniconda3/envs/pandas/lib/python3.9/site-packages/pandas/_testing.py", line 1073, in raise_assert_detail raise AssertionError(msg) AssertionError: DataFrame.index are different

DataFrame.index classes are not equivalent [left]: Index([], dtype='object') [right]: RangeIndex(start=0, stop=0, step=1)

Problem description

When creating an empty dataframe it is created with Index, and not with a RangeIndex as specified in the docs. This is a problem, e.g. in the example shown above, where I would not expect the index to change when appending the empty dataframe to itself. However, pd.testing.assert_frame_equals raises AssertionError since the indeces are not equivalent.

Expected Output

df = pd.DataFrame(columns=['a', 'b']) print(df.index) RangeIndex(start=0, stop=0, step=1)

Output of pd.show_versions()

INSTALLED VERSIONS

commit : 7d32926
python : 3.9.2.final.0
python-bits : 64
OS : Linux
OS-release : 5.4.0-59-generic
Version : #65-Ubuntu SMP Thu Dec 10 12:01:51 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.2.2
numpy : 1.20.1
pytz : 2021.1
dateutil : 2.8.1
pip : 21.0.1
setuptools : 49.6.0.post20210108
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None