BUG: ExcelWriter.book - attribute not accessible for setting

[vranoch]

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

wb = load_workbook(self._get_report_filename_template())
wb.create_sheet(self.report_range_sheet)
with pd.ExcelWriter(file, engine='openpyxl') as writer:
	writer.book = wb  # This assignment causes AttributeError: can't set attribute

Issue Description

Assignment to writer.book causes an exception:

Traceback (most recent call last): File "/app/py_code/Bussiness/Reports/PrehledovyReport.py", line 108, in _export_data writer.book = wb AttributeError: can't set attribute

downgrading to 1.4.4 resolves the issue

Expected Behavior

The assignment should work - injecting externally created workbook to the writer

Installed Versions

pd.show_versions() returns None ... presenting the requirements.txt instead

amqp==5.1.1
asgiref==3.5.2
astroid==2.12.10
asttokens==2.0.8
async-timeout==4.0.2
backports.zoneinfo==0.2.1
beautifulsoup4==4.11.1
billiard==3.6.4.0
bs4==0.0.1
celery==5.2.7
certifi==2022.9.14
chardet==5.0.0
charset-normalizer==2.1.1
click==8.1.3
click-didyoumean==0.3.0
click-plugins==1.1.1
click-repl==0.2.0
colorama==0.4.5
convertdate==2.4.0
DateTime==4.7
decorator==5.1.1
Deprecated==1.2.13
dill==0.3.5.1
Django==4.1.1
django-admin-rangefilter==0.8.8
django-appconf==1.0.5
django-celery-results==2.4.0
django-compat==1.0.15
django-debug-toolbar==3.6.0
django-imagekit==4.1.0
django-pandas==0.6.6
django-request-logging==0.7.5
django-sendgrid-v5==1.2.1
et-xmlfile==1.1.0
future==0.18.2
geocoder==1.38.1
greenlet==1.1.3
icontract==2.6.2
idna==3.4
isort==5.10.1
jdcal==1.4.1
Jinja2==3.1.2
jplephem==2.17
kombu==5.2.4
lazy-object-proxy==1.7.1
lunardate==0.2.0
MarkupSafe==2.1.1
mccabe==0.7.0
numpy==1.23.3
openpyxl==3.0.10
packaging==21.3
pandas==1.5.0
pilkit==2.0
Pillow==9.2.0
platformdirs==2.5.2
prompt-toolkit==3.0.31
psycopg2==2.9.3
pyCalverter==1.6.1
pylint==2.15.3
pylint-django==2.5.3
pylint-plugin-utils==0.7
pylint-unittest==0.1.3
pyluach==2.0.1
PyMeeus==0.5.11
pyparsing==3.0.9
pypng==0.20220715.0
PyQRCode==1.2.1
python-dateutil==2.8.2
python-http-client==3.3.7
pytz==2022.2.1
PyYAML==6.0
ratelim==0.1.6
redis==4.3.4
requests==2.28.1
sendgrid==6.9.7
sgp4==2.21
six==1.16.0
skyfield==1.45
skyfield-data==4.0.0
soupsieve==2.3.2.post1
SQLAlchemy==1.4.40
sqlparse==0.4.2
starkbank-ecdsa==2.0.3
toml==0.10.2
tomli==2.0.1
tomlkit==0.11.4
typing_extensions==4.3.0
tzdata==2022.2
urllib3==1.26.12
vine==5.0.0
wcwidth==0.2.5
workalendar==16.4.0
wrapt==1.14.1
zope.interface==5.4.0

[phofl]

Hi, thanks for your report.

All ExcelWriter attributes were considered private prior to 1.5, but this was not enforced.

We made some attributes public in 1.5, but put some restrictions on what you can do with them. For example, you can not set a book.

cc @rhshadrach to double check

[vranoch]

Hi, thanks for your report.

All ExcelWriter attributes were considered private prior to 1.5, but this was not enforced.

We made some attributes public in 1.5, but put some restrictions on what you can do with them. For example, you can not set a book.

cc @rhshadrach to double check

Hi, Thanks for Your reply, but in that case is there any legal way how to "extend" existing workbook? Without anything else, .to_excel() just overwrites given file with completely new content. The used way was to load existing workbook, create the excel writer and inject previosly loaded workbook in it. In this case all existing content of the file was preserved and new content was added.

How to achieve this functionality?

[phofl]

Could you make your example copy and passable?

You get a Workbook object from the respective engine, e.g. openpyxl. This object has methods again that you can use

[vranoch]

The following code should be reproducible (with any existing Excel file):

`
import pandas as pd
from openpyxl import load_workbook

wb = load_workbook("any_existing_nonempty_workbook.xlsx")
wb.create_sheet("range")
with pd.ExcelWriter(file, engine='openpyxl') as writer:
writer.book = wb
`

[tehunter]

I use this feature too to extend existing workbooks:

        # pandas 1.4.x; haven't tried it in 1.5 yet
        from openpyxl import load_workbook
        if (template_path and os.path.normpath(template_path) != os.path.normpath(path)):
            self.book = load_workbook(template_path)
            self.handles.handle.seek(0)
            self.sheets = {name: self.book[name] for name in self.book.sheetnames}

It's similar to using the r+ mode, but it allows you to save to a different file than the template you are loading from.

[rhshadrach]

Thanks for the report!

We made some attributes public in 1.5, but put some restrictions on what you can do with them. For example, you can not set a book.

In implementing this, we deprecated certain attributes because while they were documented as not being public, it was known that many attributes were being used by users. I think that should be the approach here - revert this in 1.5.1 allowing book to be a settable property.

However the issue with assigning a new book is that the book is stateful. Currently openpyxl doesn't use this state when writing as far as I can tell, but xlsxwriter does.

from xlsxwriter import Workbook

df = pd.DataFrame({'a': [1, 1, 2]})
df2 = pd.DataFrame({'a': [3, 3, 4]})
df.to_excel('test.xlsx', engine='xlsxwriter')

wb = Workbook('test.xlsx')

with pd.ExcelWriter('test2.xlsx', engine='xlsxwriter') as writer:
    # This is the equivalent of `writer.book = ...` in pandas 1.4.4
    writer._book = wb
    df2.to_excel(writer)

This produces test2.xlsx, but it is an empty file. It also overwrites Sheet 1 rather than adding a new sheet to test.xlsx (is this the correct behavior?). This is because unlike openpyxl, xlsxwriter uses the filename within the book when writing. It seems likely to me (but I'm not certain) that we can remove all reliance on state between method calls - i.e. any needed state within a method would be taken directly from the book or the arguments passed to ExcelWriter. I believe this would enable the setting of book safely, but maybe there are still cases of bad behavior.

[vranoch]

Hi Richard,

generally, the goal is to use existing Excel file as a template and typically add new sheets to it or write new data to existing sheets.

I understand that assigning the whole workbook anytime may be dangerous. I believe that either exposing specific "setter" method that woud correctly handle setting the object with all relevant relations - or even allowing to specify the "template" workbook only within the initialization of the writer (instead of internally setting a new workbook) would do the job.

Thanks Jan

[phofl]

Imo this is something that should be handled on the engine level, not on our side. For example:

book = writer.book
book.add_sheets(...)

This would move the functionality to openpyxl or another engine

[vranoch]

Yes, why not, but is there any way how to initialize the engine (writer.book) with an EXISTING workbook with some content, not a newly created empty one?

[phofl]

What you can do is specifying mode="a" when creating the ExcelWriter and use an existing Workbook as source, this should enable you to append to an existing workbook.