FIX: Resolve KeyError with LaTeX headers in to_latex method

Author: timapage

pandas/io/formats/style_render.py

@@ -1564,7 +1564,12 @@ def relabel_index(
         levels_ = refactor_levels(level, obj)
 
         def alias_(x, value):
+            """
+            Checks and returns formatted values based on specific conditions.
+            """
             if isinstance(value, str):
+                if value.startswith("$") and value.endswith("$"):
+                    return value
                 return value.format(x)
             return value
 

pandas/tests/io/formats/test_to_latex.py

@@ -370,6 +370,30 @@ def test_to_latex_number_of_items_in_header_missmatch_raises(
         msg = f"Writing 2 cols but got {num_aliases} aliases"
         with pytest.raises(ValueError, match=msg):
             df.to_latex(header=header)
+    
+    def test_to_latex_with_latex_header(self):
+
+        df = DataFrame({"a": [1, 2]})
+        result = df.to_latex(header=[r"$\bar{y}$"], index=False, column_format="l")
+        expected = r"""
+        \begin{tabular}{l}
+        \toprule
+        $\bar{y}$ \\
+        \midrule
+        1 \\
+        2 \\
+        \bottomrule
+        \end{tabular}
+        """
+        # Function to remove leading spaces from each line
+        def remove_leading_spaces(s):
+            return '\n'.join(line.lstrip() for line in s.strip().split('\n'))
+
+        # Normalize both result and expected strings
+        result_clean = remove_leading_spaces(result)
+        expected_clean = remove_leading_spaces(expected)
+
+        assert result_clean == expected_clean, f"Result:\n{repr(result)}\nExpected:\n{repr(expected)}"
 
     def test_to_latex_decimal(self):
         # GH 12031