PR fixes

Author: jsngn

pandas/core/reshape/encoding.py

@@ -183,7 +183,9 @@ def check_len(item, name: str) -> None:
         check_len(prefix_sep, "prefix_sep")
 
         if isinstance(prefix, str):
-            prefix = itertools.cycle([prefix])
+            prefix = itertools.islice(
+                itertools.cycle([prefix]), data_to_encode.shape[1]
+            )
         if isinstance(prefix, dict):
             prefix = [prefix[col] for col in data_to_encode.columns]
 
@@ -192,7 +194,9 @@ def check_len(item, name: str) -> None:
 
         # validate separators
         if isinstance(prefix_sep, str):
-            prefix_sep = itertools.cycle([prefix_sep])
+            prefix_sep = itertools.islice(
+                itertools.cycle([prefix_sep]), data_to_encode.shape[1]
+            )
         elif isinstance(prefix_sep, dict):
             prefix_sep = [prefix_sep[col] for col in data_to_encode.columns]
 
@@ -210,7 +214,7 @@ def check_len(item, name: str) -> None:
             with_dummies = [data.select_dtypes(exclude=dtypes_to_encode)]
 
         for col, pre, sep in zip(
-            data_to_encode.items(), prefix, prefix_sep, strict=False
+            data_to_encode.items(), prefix, prefix_sep, strict=True
         ):
             # col is (column_name, column), use just column data here
             dummy = _get_dummies_1d(

pandas/core/reshape/reshape.py

@@ -780,7 +780,7 @@ def _stack_multi_column_index(columns: MultiIndex) -> MultiIndex | Index:
 
     levs = (
         [lev[c] if c >= 0 else None for c in codes]
-        for lev, codes in zip(columns.levels[:-1], columns.codes[:-1], strict=False)
+        for lev, codes in zip(columns.levels[:-1], columns.codes[:-1], strict=True)
     )
 
     # Remove duplicate tuples in the MultiIndex.