Add support for unary plus and unary minus to collections.Counter()
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index f344b5a..df231f8 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -264,7 +264,7 @@
c.items() # convert to a list of (elem, cnt) pairs
Counter(dict(list_of_pairs)) # convert from a list of (elem, cnt) pairs
c.most_common()[:-n:-1] # n least common elements
- c += Counter() # remove zero and negative counts
+ +c # remove zero and negative counts
Several mathematical operations are provided for combining :class:`Counter`
objects to produce multisets (counters that have counts greater than zero).
@@ -284,6 +284,18 @@
>>> c | d # union: max(c[x], d[x])
Counter({'a': 3, 'b': 2})
+Unary addition and substraction are shortcuts for adding an empty counter
+or subtracting from an empty counter.
+
+ >>> c = Counter(a=2, b=-4)
+ >>> +c
+ Counter({'a': 2})
+ >>> -c
+ Counter({'b': 4})
+
+.. versionadded:: 3.3
+ Added support for unary plus and unary minus.
+
.. note::
Counters were primarily designed to work with positive integers to represent