TYP: define gen and gen2 as Iterable

Author: Kashif Khan

pandas/io/formats/excel.py

@@ -649,12 +649,15 @@ def _format_header_regular(self) -> Iterable[ExcelCell]:
  )
 
  def _format_header(self) -> Iterable[ExcelCell]:
+ gen: Iterable[ExcelCell]
+
  if isinstance(self.columns, MultiIndex):
  gen = self._format_header_mi()
  else:
  gen = self._format_header_regular()
 
- gen2 = ()
+ gen2: Iterable[ExcelCell] | tuple[()] = ()
+
  if self.df.index.names:
  row = [x if x is not None else "" for x in self.df.index.names] + [
  ""