BUG: Styler cannot accept semicolon in CSS val

[tehunter]

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• 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

df = pd.DataFrame({"A": [1, 0, -1]})

css = 'text-align: left; number-format: "0;[Red](0);-;@"; ;'

try:
    (
        df
        .style
        # Replace zero with dash, negative with red
        .applymap(lambda x: css)
        .to_excel("test.xlsx")
    )
except Exception as e:
    print(e)

Issue Description

Styler does not accept CSS value string types enclosed in double quotes. In particular, it crashes if the string contains semi-colons. This means full number-format strings cannot be passed to Styler for exporting to Excel. Excel number format is of the form: <positive>;<negative>;<zero>;<text>. The semi-colon dividers here will conflict with CSS semi-colon dividers unless they can be properly encapsulated in a string.

The problem is rooted in the naive string split in maybe_convert_css_to_tuples and CSSResolver. A possible fix using the TextFileReader parser is shown in the Expected Behavior section.

Expected Behavior

In the above example, the function should export the following sheet:

Here is a set of changes that can produce the desired behavior using pandas parsing libraries:

### In style_render.py
def maybe_convert_css_to_tuples(style):
    from io import StringIO
    from pandas.io.parsers.readers import TextFileReader

    if style and isinstance(style, str):
        # Use "C" parser because of line terminator
        s = TextFileReader(StringIO(style), engine="c", delimiter=":", lineterminator=";", skipinitialspace=True, index=False, header=None).read()

        try:
            return [
                (row[0].strip(), row[1].strip())
                for _, row in s.iterrows()
                if row[0] != ""
            ]
        except IndexError:
            raise ValueError(
                "Styles supplied as string must follow CSS rule formats, "
                f"for example 'attr: val;'. '{style}' was given."
            )
    return style

### In css.py
class CSSResolver():
    # ...
    def parse(self, declarations_str: str):
        from io import StringIO
        from pandas.io.parsers.c_parser_wrapper import CParserWrapper
        from pandas.io.parsers.readers import TextFileReader

        if (declarations_str):
            s = TextFileReader(StringIO(declarations_str), engine="c", delimiter=":", lineterminator=";", skipinitialspace=True, index=False, header=None).read()

            try:
                for _,row in s.iterrows():
                    prop, val = row[0], row[1]

                    prop = prop.strip().lower()
                    # TODO: don't lowercase case sensitive parts of values (strings)
                    val = val.strip().lower()

                    yield prop, val
            except Exception as e:
                print(e)

### In io/formats/excel.py
class CssExcelCell(ExcelCell):
    def __init__(
        self,
        row: int,
        col: int,
        val,
        style: dict | None,
        css_styles: dict[tuple[int, int], list[tuple[str, Any]]] | None,
        css_row: int,
        css_col: int,
        css_converter: Callable | None,
        **kwargs,
    ):
        if css_styles and css_converter:
            # Not exhaustively tested. Might be better to add quotes conditionally based on type of `v`
            css = ";".join(a + ":" + "\"" + str(v) + "\"" for (a, v) in css_styles[css_row, css_col])
            style = css_converter(css)

        return super().__init__(row=row, col=col, val=val, style=style, **kwargs)

Installed Versions

INSTALLED VERSIONS

commit : 06d2301
python : 3.10.1.final.0
python-bits : 64
OS : Windows
OS-release : 10
...
pandas : 1.4.1
numpy : 1.22.0
pytz : 2021.3
dateutil : 2.8.2
pip : 22.0.3
setuptools : 60.2.0
Cython : None
pytest : 7.0.1
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 3.0.2
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.0.0
pandas_datareader: None
bs4 : None
bottleneck : 1.3.2
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.5.1
numba : None
numexpr : 2.8.0
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.7.3
sqlalchemy : None
tables : 3.6.1
tabulate : None
xarray : None
xlrd : 2.0.1
xlwt : None
zstandard : None

[tehunter]

Related to #42276

[attack68]

if you are considering a solution a similar issue arises for LaTeX captions, which use a colon. The solution was in _parse_latex_table_styles

    Notes
    -----
    The replacement of "§" with ":" is to avoid the CSS problem where ":" has structural
    significance and cannot be used in LaTeX labels, but is often required by them.
    """
    for style in table_styles[::-1]:  # in reverse for most recently applied style
        if style["selector"] == selector:
            return str(style["props"][0][1]).replace("§", ":")
    return None

[attack68]

Since CSS is a specific language a need to parse semi-colons and colons differently is not required, imo.

The number-format css attribute is a pandas construct to hack the to_excel output. Since it is a pandas construct we can direct users how to interact with it so that it works. See the PR and comment if you object.