X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=list_utils.py;h=71630dc9a6fdb4d968f890b2ac4d3b8cb78360d2;hb=a4bf4d05230474ad14243d67ac7f8c938f670e58;hp=992f1ae4207228711c17573bb779cc0aaae2d0f8;hpb=5f75cf834725ac26b289cc5f157af0cb71cd5f0e;p=python_utils.git

diff --git a/list_utils.py b/list_utils.py
index 992f1ae..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
@@ -197,12 +197,12 @@ def ngrams(lst: Sequence[Any], n):
     ['an', 'awesome', 'test']
     """
     for i in range(len(lst) - n + 1):
-        yield lst[i:i + 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)
@@ -216,19 +216,23 @@ 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:]
+        right = seq[i + 1 :]
         cdr = left + right
         yield from _permute(cdr, path + car)
 
 
-def binary_search(lst: Sequence[Any], target:Any) -> Tuple[bool, int]:
+def binary_search(
+    lst: Sequence[Any], target: Any, *, sanity_check=False
+) -> Tuple[bool, int]:
     """Performs a binary search on lst (which must already be sorted).
     Returns a Tuple composed of a bool which indicates whether the
     target was found and an int which indicates the index closest to
@@ -247,11 +251,25 @@ def binary_search(lst: Sequence[Any], target:Any) -> Tuple[bool, int]:
     >>> binary_search(a, 2)
     (False, 1)
 
+    >>> a.append(9)
+    >>> binary_search(a, 4, sanity_check=True)
+    Traceback (most recent call last):
+    ...
+    AssertionError
+
     """
+    if sanity_check:
+        last = None
+        for x in lst:
+            if last is not None:
+                assert x >= last  # This asserts iff the list isn't sorted
+            last = x  # in ascending order.
     return _binary_search(lst, target, 0, len(lst) - 1)
 
 
-def _binary_search(lst: Sequence[Any], target: Any, low: int, high: int) -> Tuple[bool, int]:
+def _binary_search(
+    lst: Sequence[Any], target: Any, low: int, high: int
+) -> Tuple[bool, int]:
     if high >= low:
         mid = (high + low) // 2
         if lst[mid] == target:
@@ -266,4 +284,5 @@ def _binary_search(lst: Sequence[Any], target: Any, low: int, high: int) -> Tupl
 
 if __name__ == '__main__':
     import doctest
+
     doctest.testmod()