BUG: ExcelWriter: file is corrupted on save (and: does it accept a file object?)

• I have checked that this issue has not already been reported.

• 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.

---

Code Sample, a copy-pastable example

first.py:

import pandas as pd
import openpyxl

df = pd.DataFrame(data={'col1': [1, 2], 'col2': [3, 4]})

writer1 = pd.ExcelWriter('first.xlsx', engine='openpyxl')
df.to_excel(writer1)
writer1.save()
writer1.close()

second.py:

import pandas as pd
import openpyxl

df = pd.DataFrame(data={'col1': [1, 2], 'col2': [3, 4]})

output2 = open('second.xlsx', 'wb')
writer2 = pd.ExcelWriter(output2, engine='openpyxl')
df.to_excel(writer2)
writer2.save()
writer2.close()
output2.flush()
output2.close()

UPD 2:

writer2.save()
writer2.close()

Remove one line. It will start to work!

UPD: third.py (see https://github.com/pandas-dev/pandas/issues/33746#issuecomment-640169769 by @lordgrenville):

import pandas as pd
import openpyxl

df = pd.DataFrame(data={'col1': [1, 2], 'col2': [3, 4]})

with open('third.xlsx', 'wb') as output3:
    writer3 = pd.ExcelWriter(output3, engine='openpyxl')
    df.to_excel(writer3)
    writer3.save()

Problem description

$ python first.py
$ python second.py
$ du -b first.xlsx second.xlsx third.xlsx
4737	first.xlsx
9474	second.xlsx
4737	third.xlsx

~(Note: 9474 = 2 * 4737. But sometimes it’s not true.)~

1. Why files differ?
2. Documentation says: path - str - Path to xls or xlsx file. So does pd.ExcelWriter.__init__ accept a file-like object?

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None python : 3.7.7.final.0 python-bits : 64 OS : Linux OS-release : 5.4.32-calculate machine : x86_64 processor : Intel® Core™ i5-7200U CPU @ 2.50GHz byteorder : little LC_ALL : None LANG : ru_RU.utf8 LOCALE : ru_RU.UTF-8

pandas : 1.0.3 numpy : 1.18.1 pytz : 2019.3 dateutil : 2.8.1 pip : 20.0.2 setuptools : 46.1.3.post20200330 Cython : 0.29.15 pytest : None hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : 1.2.8 lxml.etree : 4.5.0 html5lib : None pymysql : None psycopg2 : None jinja2 : 2.11.1 IPython : 7.13.0 pandas_datareader: None bs4 : None bottleneck : None fastparquet : None gcsfs : None lxml.etree : 4.5.0 matplotlib : 3.1.3 numexpr : None odfpy : None openpyxl : 3.0.3 pandas_gbq : None pyarrow : None pytables : None pytest : None pyxlsb : None s3fs : None scipy : 1.4.1 sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlwt : None xlsxwriter : 1.2.8 numba : None

[wwwald]

I’m running into the same problem, or at least it seems very similar.

In my case, I’m trying to write a dataframe to an existing worksheet, using ExcelWriter’s append mode. When opening the resulting file excel-results.xlsx, Excel (Office 365) warns me that it is corrupt and offers to repair. The repair does work, but of course, it shouldn’t be necessary.

Some code to reproduce the problem:

import pandas as pd
from pathlib import Path
import shutil
from openpyxl import load_workbook

xlsx_template = Path("excel-template.xlsx")
xlsx_results = Path("excel-results.xlsx")
shutil.copy2(xlsx_template, xlsx_results)

df = pd.DataFrame(
    {"type": ["ERROR", "NOTFOUND", "ERROR"], 
     "message": ["First error message", "Didn't find a value", "Another error"]}
)

with pd.ExcelWriter(xlsx_results, engine="openpyxl", mode="a") as writer:
    writer.book = load_workbook(xlsx_results)
    writer.sheets = {ws.title: ws for ws in writer.book.worksheets}
    df.to_excel(writer, sheet_name="Error messages", startrow=7, startcol=1, index=False, header=False)
    writer.save()

The excel-template.xlsx file used here is this one.

Versions used to reproduce this:

INSTALLED VERSIONS  
------------------  
commit           : 2cb96529396d93b46abab7bbc73a208e708c642e  
python           : 3.7.10.final.0  
python-bits      : 64  
OS               : Windows  
OS-release       : 10  
Version          : 10.0.17763  
machine          : AMD64  
processor        : Intel64 Family 6 Model 158 Stepping 10, GenuineIntel  
byteorder        : little  
LC_ALL           : None  
LANG             : en_US.UTF-8  
LOCALE           : None.None  
  
pandas           : 1.2.4  
numpy            : 1.20.2  
pytz             : 2021.1  
dateutil         : 2.8.1  
pip              : 21.1.1  
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         : 3.0.7  
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  

[kuraga]

writer2.save()
writer2.close()

Remove one line. It will start to work!