Fix Excel-specific border styles (#48660)

* Add tests * Add support for "hair" style * Support excel-specific border styles * Use black border if styled but color unspecified * Added documentation and whatsnew * Black linter * Fixed tests for Excel border color fallback * Revert style.ipynb metadata * Fix typo * Revert border-color default value * Revert "Fixed tests for Excel border color fallback" This reverts commit d2680ef. * Revert border color default tests * Updated whatsnew entry * Add method link to whatsnew * Add tests and fix case sensitivity * Apply black linter * Update v1.5.2.rst * Fix documentation typo * Test that border shorthand works * Append Excel styles to shorthand parsing * Update to find_stack_level call * Update v1.5.3.rst

Author: tehunter

doc/source/user_guide/style.ipynb

@@ -1594,8 +1594,9 @@
  "\n",
  "\n",
  "- Only CSS2 named colors and hex colors of the form `#rgb` or `#rrggbb` are currently supported.\n",
- "- The following pseudo CSS properties are also available to set excel specific style properties:\n",
+ "- The following pseudo CSS properties are also available to set Excel specific style properties:\n",
  " - `number-format`\n",
+ " - `border-style` (for Excel-specific styles: \"hair\", \"mediumDashDot\", \"dashDotDot\", \"mediumDashDotDot\", \"dashDot\", \"slantDashDot\", or \"mediumDashed\")\n",
  "\n",
  "Table level styles, and data cell CSS-classes are not included in the export to Excel: individual cells must have their properties mapped by the `Styler.apply` and/or `Styler.applymap` methods."
  ]

doc/source/whatsnew/v1.5.3.rst

@@ -24,7 +24,7 @@ Fixed regressions
 
 Bug fixes
 ~~~~~~~~~
--
+- Bug in :meth:`.Styler.to_excel` leading to error when unrecognized ``border-style`` (e.g. ``"hair"``) provided to Excel writers (:issue:`48649`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/io/formats/css.py

@@ -105,9 +105,9 @@ def expand(self, prop, value: str) -> Generator[tuple[str, str], None, None]:
  f"border{side}-width": "medium",
  }
  for token in tokens:
- if token in self.BORDER_STYLES:
+ if token.lower() in self.BORDER_STYLES:
  border_declarations[f"border{side}-style"] = token
- elif any(ratio in token for ratio in self.BORDER_WIDTH_RATIOS):
+ elif any(ratio in token.lower() for ratio in self.BORDER_WIDTH_RATIOS):
  border_declarations[f"border{side}-width"] = token
  else:
  border_declarations[f"border{side}-color"] = token
@@ -181,6 +181,13 @@ class CSSResolver:
  "ridge",
  "inset",
  "outset",
+ "mediumdashdot",
+ "dashdotdot",
+ "hair",
+ "mediumdashdotdot",
+ "dashdot",
+ "slantdashdot",
+ "mediumdashed",
  ]
 
  SIDE_SHORTHANDS = {

pandas/io/formats/excel.py

@@ -159,6 +159,22 @@ class CSSToExcelConverter:
  "fantasy": 5, # decorative
  }
 
+ BORDER_STYLE_MAP = {
+ style.lower(): style
+ for style in [
+ "dashed",
+ "mediumDashDot",
+ "dashDotDot",
+ "hair",
+ "dotted",
+ "mediumDashDotDot",
+ "double",
+ "dashDot",
+ "slantDashDot",
+ "mediumDashed",
+ ]
+ }
+
  # NB: Most of the methods here could be classmethods, as only __init__
  # and __call__ make use of instance attributes. We leave them as
  # instancemethods so that users can easily experiment with extensions
@@ -306,6 +322,16 @@ def _border_style(self, style: str | None, width: str | None, color: str | None)
  if width_name in ("hair", "thin"):
  return "dashed"
  return "mediumDashed"
+ elif style in self.BORDER_STYLE_MAP:
+ # Excel-specific styles
+ return self.BORDER_STYLE_MAP[style]
+ else:
+ warnings.warn(
+ f"Unhandled border style format: {repr(style)}",
+ CSSWarning,
+ stacklevel=find_stack_level(),
+ )
+ return "none"
 
  def _get_width_name(self, width_input: str | None) -> str | None:
  width = self._width_to_float(width_input)

pandas/tests/io/excel/test_style.py

@@ -115,6 +115,12 @@ def test_styler_to_excel_unstyled(engine):
  ["border", "left", "color", "rgb"],
  {"xlsxwriter": "FF111222", "openpyxl": "00111222"},
  ),
+ # Border styles
+ (
+ "border-left-style: hair; border-left-color: black",
+ ["border", "left", "style"],
+ "hair",
+ ),
 ]
 
 
@@ -196,6 +202,62 @@ def test_styler_to_excel_basic_indexes(engine, css, attrs, expected):
  assert sc_cell == expected
 
 
+# From https://openpyxl.readthedocs.io/en/stable/api/openpyxl.styles.borders.html
+# Note: Leaving behavior of "width"-type styles undefined; user should use border-width
+# instead
+excel_border_styles = [
+ # "thin",
+ "dashed",
+ "mediumDashDot",
+ "dashDotDot",
+ "hair",
+ "dotted",
+ "mediumDashDotDot",
+ # "medium",
+ "double",
+ "dashDot",
+ "slantDashDot",
+ # "thick",
+ "mediumDashed",
+]
+
+
+@pytest.mark.parametrize(
+ "engine",
+ ["xlsxwriter", "openpyxl"],
+)
+@pytest.mark.parametrize("border_style", excel_border_styles)
+def test_styler_to_excel_border_style(engine, border_style):
+ css = f"border-left: {border_style} black thin"
+ attrs = ["border", "left", "style"]
+ expected = border_style
+
+ pytest.importorskip(engine)
+ df = DataFrame(np.random.randn(1, 1))
+ styler = df.style.applymap(lambda x: css)
+
+ with tm.ensure_clean(".xlsx") as path:
+ with ExcelWriter(path, engine=engine) as writer:
+ df.to_excel(writer, sheet_name="dataframe")
+ styler.to_excel(writer, sheet_name="styled")
+
+ openpyxl = pytest.importorskip("openpyxl") # test loading only with openpyxl
+ with contextlib.closing(openpyxl.load_workbook(path)) as wb:
+
+ # test unstyled data cell does not have expected styles
+ # test styled cell has expected styles
+ u_cell, s_cell = wb["dataframe"].cell(2, 2), wb["styled"].cell(2, 2)
+ for attr in attrs:
+ u_cell, s_cell = getattr(u_cell, attr, None), getattr(s_cell, attr)
+
+ if isinstance(expected, dict):
+ assert u_cell is None or u_cell != expected[engine]
+ assert s_cell == expected[engine]
+ else:
+ assert u_cell is None or u_cell != expected
+ assert s_cell == expected
+
+
 def test_styler_custom_converter():
  openpyxl = pytest.importorskip("openpyxl")