Pandas BUG: df.to_excel fails for "border-style: hair" with xlsxwriter

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Reproducible Example

import pandas as pd

df = pd.DataFrame({"a": [1]})
styler = df.style.applymap(lambda x: "border-style: hair; border-color: black")

styler.to_excel(r"test_border.xlsx", engine="xlsxwriter")

Issue Description

The CSSToExcelConverter._border_style function does not return any value (i.e., None) when the style string is not recognized. However, "hair" should be a recognized style string in xlsxwriter, corresponding to border index "7". This leads to a crash in xlsxwriter. Moreover, there is no path to actually return the "hair" style for any engine.

Expected Behavior

Use of border-style: hair will export a spreadsheet with the correct formatting.

Installed Versions

INSTALLED VERSIONS ------------------ commit : 224458ee25d92ccdf289d1ae2741d178df4f323e python : 3.10.4.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19044 machine : AMD64 processor : Intel64 Family 6 Model 142 Stepping 12, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : English_United States.1252 pandas : 1.5.0rc0 numpy : 1.21.6 pytz : 2022.1 dateutil : 2.8.2 setuptools : 63.4.1 pip : 22.1.2 Cython : None pytest : 7.1.2 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : 3.0.3 lxml.etree : 4.9.1 html5lib : None pymysql : None psycopg2 : None jinja2 : 3.1.2 IPython : 8.4.0 pandas_datareader: None bs4 : 4.11.1 bottleneck : 1.3.5 brotli : None fastparquet : 0.5.0 fsspec : None gcsfs : None matplotlib : None numba : 0.55.2 numexpr : 2.8.3 odfpy : None openpyxl : 3.0.10 pandas_gbq : None pyarrow : 8.0.0 pyreadstat : 1.1.9 pyxlsb : None s3fs : None scipy : None snappy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : 2.0.1 xlwt : None zstandard : None tzdata : None

Comment From: tehunter

take

Comment From: rhshadrach

Thanks for the report @tehunter! Your versions indicate 1.5.0rc; do you know if this bug exists in previous versions?

Comment From: tehunter

I know that previous versions also had an inability to use the "hair" style. I'm unsure at the moment if it led to the same error. I think it probably gave the same error identified here and in #45312.

In addition to adding support for the "hair" style, I think we probably need to have a "soft fail" for unrecognized/unimplemented border combinations. I'll work on adding both in a PR.

Comment From: rhshadrach

However, "hair" should be a recognized style string in xlsxwriter, corresponding to border index "1"

Why not index 7? Does weight 0 mean that there is no visible border for index 7?