ENH: Enable cleaning of unnamed columns for CSV parsers and adjust strictness in zip() calls

Author: allamlobna

pandas/io/parsers/base_parser.py

@@ -237,9 +237,11 @@ def _extract_multi_indexer_columns(
         def extract(r):
             return tuple(r[i] for i in range(field_count) if i not in sic)
 
-        columns = list(zip(*(extract(r) for r in header), strict=False))
-        # Clean the columns by removing placeholders.
-        columns = self._clean_column_levels(columns)
+        columns = list(zip(*(extract(r) for r in header), strict=True))
+
+        # Clean unnamed placeholders for CSV parsers only (GH#59560)
+        if getattr(self, "_clean_csv_unnamed_columns", False):
+            columns = self._clean_column_levels(columns)
 
         names = columns.copy()
         for single_ic in sorted(ic):
@@ -732,7 +734,7 @@ def _is_generated_unnamed(level: str | None) -> bool:
                 ""
                 if (
                     level is None
-                    or str(level).strip() == ""
+                    or (isinstance(level, str) and level.strip() == "")
                     or _is_generated_unnamed(level)
                 )
                 else level

pandas/io/parsers/c_parser_wrapper.py

@@ -64,6 +64,7 @@ class CParserWrapper(ParserBase):
 
     def __init__(self, src: ReadCsvBuffer[str], **kwds) -> None:
         super().__init__(kwds)
+        self._clean_csv_unnamed_columns = True
         self.kwds = kwds
         kwds = kwds.copy()
 

pandas/io/parsers/python_parser.py

@@ -101,7 +101,9 @@ def __init__(self, f: ReadCsvBuffer[str] | list, **kwds) -> None:
         Workhorse function for processing nested list into DataFrame
         """
         super().__init__(kwds)
-
+        # Only enable cleaning for CSV (file/buffer), not Excel (list)
+        if not isinstance(f, list) and "has_index_names" not in kwds:
+            self._clean_csv_unnamed_columns = True
         self.data: Iterator[list[str]] | list[list[Scalar]] = []
         self.buf: list = []
         self.pos = 0