feat: make addition of ToC idempotent

By design it was possible to add table of contents multiple times.
The rendered report then contained multiple table of contents.
Having a separate argument for table of contents instead of having
it in sections list makes multiple calls of add_table_of_contents()
idempotent — always only one ToC is rendered in the end.

edvart/report.py

@@ -46,14 +46,14 @@ def __init__(
         self.df = dataframe
         self.sections: list[Section] = []
         self.verbosity = Verbosity(verbosity)
+        self._table_of_contents = None
 
     def show(self) -> None:
         """Renders the report in the calling notebook."""
+        if self._table_of_contents is not None:
+            self._table_of_contents.show(self.sections)
         for section in self.sections:
-            if isinstance(section, TableOfContents):
-                section.show(self.sections)
-            else:
-                section.show(self.df)
+            section.show(self.df)
 
     def _select_columns(
         self,
@@ -173,11 +173,10 @@ def _generate_notebook(
         nb["cells"].append(nbf4.new_code_cell(load_df))
 
         # Generate code for each report section
+        if self._table_of_contents is not None:
+            self._table_of_contents.add_cells(self.sections, nb["cells"])
         for section in self.sections:
-            if isinstance(section, TableOfContents):
-                section.add_cells(self.sections, nb["cells"])
-            else:
-                section.add_cells(nb["cells"])
+            section.add_cells(nb["cells"])
 
         return nb
 
@@ -592,7 +591,7 @@ def add_table_of_contents(self, include_subsections: bool = True) -> "ReportBase
             contents. However, they won't be included in an exported notebook created by report's
             export_notebook function.
         """
-        self.sections.append(TableOfContents(include_subsections))
+        self._table_of_contents = TableOfContents(include_subsections)
         return self
 
 

edvart/report_sections/table_of_contents.py

@@ -89,8 +89,7 @@ def add_cells(self, sections: List[Section], cells: List[Dict[str, Any]]) -> Non
         # Add links to all main sections (not including subsections) besides the first (table of
         # content) section
         for section in sections:
-            if not isinstance(section, TableOfContents):
-                lines.append(TableOfContents._get_section_link(section, 1))
+            lines.append(TableOfContents._get_section_link(section, 1))
         cells.append(nbfv4.new_markdown_cell("\n".join(lines)))
 
     # pylint: disable=arguments-renamed
@@ -108,6 +107,5 @@ def show(self, sections: List[Section]) -> None:
         # Add links to all sections including their subsections besides the first (table of content)
         # section
         for section in sections:
-            if not isinstance(section, TableOfContents):
-                self._add_section_lines(section, 1, lines, self._include_subsections)
+            self._add_section_lines(section, 1, lines, self._include_subsections)
         display(Markdown("\n".join(lines)))