Clean up mypy type checker errors.

1 files changed, 7 insertions, 6 deletions

diff --git a/list_utils.py b/list_utils.py
index b65ab0d..71630dc 100644
--- a/list_utils.py
+++ b/list_utils.py
@@ -65,7 +65,7 @@ def remove_list_if_one_element(lst: List[Any]) -> Any:
         return lst
 
 
-def population_counts(lst: List[Any]) -> Mapping[Any, int]:
+def population_counts(lst: List[Any]) -> Counter:
     """
     Return a population count mapping for the list (i.e. the keys are
     list items and the values are the number of occurrances of that
@@ -200,9 +200,9 @@ def ngrams(lst: Sequence[Any], n):
         yield lst[i : i + n]
 
 
-def permute(seq: Sequence[Any]):
+def permute(seq: str):
     """
-    Returns all permutations of a sequence; takes O(N^2) time.
+    Returns all permutations of a sequence; takes O(N!) time.
 
     >>> for x in permute('cat'):
     ...     print(x)
@@ -217,11 +217,12 @@ def permute(seq: Sequence[Any]):
     yield from _permute(seq, "")
 
 
-def _permute(seq: Sequence[Any], path):
-    if len(seq) == 0:
+def _permute(seq: str, path: str):
+    seq_len = len(seq)
+    if seq_len == 0:
         yield path
 
-    for i in range(len(seq)):
+    for i in range(seq_len):
         car = seq[i]
         left = seq[0:i]
         right = seq[i + 1 :]