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authorRaymond Hettinger <rhettinger@users.noreply.github.com>2022-02-01 22:18:11 -0600
committerGitHub <noreply@github.com>2022-02-01 22:18:11 -0600
commitf77beacf015e9bf8762e9b9a9a631396b05d4d9a (patch)
tree08c4c61e51bcb1c620fbbda45f2526e0e1fbdd0d
parentabcc3d75f6e570519cb37c62130a2295c6928bff (diff)
downloadcpython-git-f77beacf015e9bf8762e9b9a9a631396b05d4d9a.tar.gz
Fix minor details in the Counter docs (GH-31029)
-rw-r--r--Doc/library/collections.rst13
-rw-r--r--Lib/collections/__init__.py4
2 files changed, 14 insertions, 3 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index b8a717d883..b97bc425de 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -271,7 +271,7 @@ For example::
.. versionadded:: 3.1
.. versionchanged:: 3.7 As a :class:`dict` subclass, :class:`Counter`
- Inherited the capability to remember insertion order. Math operations
+ inherited the capability to remember insertion order. Math operations
on *Counter* objects also preserve order. Results are ordered
according to when an element is first encountered in the left operand
and then by the order encountered in the right operand.
@@ -366,19 +366,26 @@ Several mathematical operations are provided for combining :class:`Counter`
objects to produce multisets (counters that have counts greater than zero).
Addition and subtraction combine counters by adding or subtracting the counts
of corresponding elements. Intersection and union return the minimum and
-maximum of corresponding counts. Each operation can accept inputs with signed
+maximum of corresponding counts. Equality and inclusion compare
+corresponding counts. Each operation can accept inputs with signed
counts, but the output will exclude results with counts of zero or less.
+.. doctest::
+
>>> c = Counter(a=3, b=1)
>>> d = Counter(a=1, b=2)
>>> c + d # add two counters together: c[x] + d[x]
Counter({'a': 4, 'b': 3})
>>> c - d # subtract (keeping only positive counts)
Counter({'a': 2})
- >>> c & d # intersection: min(c[x], d[x]) # doctest: +SKIP
+ >>> c & d # intersection: min(c[x], d[x])
Counter({'a': 1, 'b': 1})
>>> c | d # union: max(c[x], d[x])
Counter({'a': 3, 'b': 2})
+ >>> c == d # equality: c[x] == d[x]
+ False
+ >>> c <= d # inclusion: c[x] <= d[x]
+ False
Unary addition and subtraction are shortcuts for adding an empty counter
or subtracting from an empty counter.
diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index fa8b30985a..264435cb41 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -736,6 +736,10 @@ class Counter(dict):
# To strip negative and zero counts, add-in an empty counter:
# c += Counter()
#
+ # Results are ordered according to when an element is first
+ # encountered in the left operand and then by the order
+ # encountered in the right operand.
+ #
# When the multiplicities are all zero or one, multiset operations
# are guaranteed to be equivalent to the corresponding operations
# for regular sets.