CLN: add arg validation for caption

doc/source/whatsnew/v1.4.0.rst

@@ -83,6 +83,8 @@ Formerly Styler relied on ``display.html.use_mathjax``, which has now been repla
 
 There are also bug fixes and deprecations listed below.
 
+Validation now for ``caption`` arg (:issue:`43368`)
+
 .. _whatsnew_140.enhancements.pyarrow_csv_engine:
 
 Multithreaded CSV reading with a new CSV Engine based on pyarrow

pandas/io/formats/style.py

@@ -1773,6 +1773,16 @@ def set_caption(self, caption: str | tuple) -> Styler:
         -------
         self : Styler
         """
+        msg = "`caption` must be either a string or 2-tuple of strings."
+        if isinstance(caption, tuple):
+            if (
+                len(caption) != 2
+                or not isinstance(caption[0], str)
+                or not isinstance(caption[1], str)
+            ):
+                raise ValueError(msg)
+        elif not isinstance(caption, str):
+            raise ValueError(msg)
         self.caption = caption
         return self
 

pandas/tests/io/formats/style/test_style.py

@@ -1439,3 +1439,10 @@ def test_hidden_column_names(mi_df):
     ctx = mi_styler._translate(True, True)
     assert len(ctx["head"]) == 1  # no index names and only one visible column headers
     assert ctx["head"][0][1]["display_value"] == " "
+
+
+@pytest.mark.parametrize("caption", [1, ("a", "b", "c"), (1, "s")])
+def test_caption_raises(mi_styler, caption):
+    msg = "`caption` must be either a string or 2-tuple of strings."
+    with pytest.raises(ValueError, match=msg):
+        mi_styler.set_caption(caption)