Introduce viewkeys(), viewvalues(), and viewitems().

Closes issue #92

4 files changed, 73 insertions, 0 deletions

diff --git a/.hgignore b/.hgignore
index 2a22acf..8815294 100644
--- a/.hgignore
+++ b/.hgignore
@@ -4,3 +4,4 @@ dist
 MANIFEST
 documentation/_build
 .tox
+six.egg-info
diff --git a/documentation/index.rst b/documentation/index.rst
index 0adadc2..594976b 100644
--- a/documentation/index.rst
+++ b/documentation/index.rst
@@ -203,6 +203,27 @@ functions and methods is the stdlib :mod:`py3:inspect` module.
    *kwargs* are passed through to the underlying method.
 
 
+.. function:: viewkeys(dictionary, **kwargs)
+
+   Returns a view over *dictionary*\'s keys. This replaces
+   ``dictionary.viewkeys()`` on Python 2.7 and ``dictionary.keys()`` on
+   Python 3. *kwargs* are passed through to the underlying method.
+
+
+.. function:: viewvalues(dictionary, **kwargs)
+
+   Returns a view over *dictionary*\'s values. This replaces
+   ``dictionary.viewvalues()`` on Python 2.7 and ``dictionary.values()`` on
+   Python 3. *kwargs* are passed through to the underlying method.
+
+
+.. function:: viewitems(dictionary, **kwargs)
+
+   Returns a view over *dictionary*\'s items. This replaces
+   ``dictionary.viewitems()`` on Python 2.7 and ``dictionary.items()`` on
+   Python 3. *kwargs* are passed through to the underlying method.
+
+
 .. function:: create_bound_method(func, obj)
 
    Return a method object wrapping *func* and bound to *obj*.  On both Python 2
diff --git a/six.py b/six.py
index 21b0e80..5efb62b 100644
--- a/six.py
+++ b/six.py
@@ -554,6 +554,15 @@ if PY3:
 
     def iterlists(d, **kw):
         return iter(d.lists(**kw))
+
+    def viewkeys(d, **kw):
+        return d.keys(**kw)
+
+    def viewvalues(d, **kw):
+        return d.values(**kw)
+
+    def viewitems(d, **kw):
+        return d.items(**kw)
 else:
     def iterkeys(d, **kw):
         return iter(d.iterkeys(**kw))
@@ -567,12 +576,25 @@ else:
     def iterlists(d, **kw):
         return iter(d.iterlists(**kw))
 
+    def viewkeys(d, **kw):
+        return d.viewkeys(**kw)
+
+    def viewvalues(d, **kw):
+        return d.viewvalues(**kw)
+
+    def viewitems(d, **kw):
+        return d.viewitems(**kw)
+
 _add_doc(iterkeys, "Return an iterator over the keys of a dictionary.")
 _add_doc(itervalues, "Return an iterator over the values of a dictionary.")
 _add_doc(iteritems,
          "Return an iterator over the (key, value) pairs of a dictionary.")
 _add_doc(iterlists,
          "Return an iterator over the (key, [values]) pairs of a dictionary.")
+_add_doc(viewkeys, "Return a view over the keys of a dictionary.")
+_add_doc(viewvalues, "Retun a view over the values of a dictionary.")
+_add_doc(viewitems,
+         "Return a view over the (key, value) pairs of a dictionary.")
 
 
 if PY3:
diff --git a/test_six.py b/test_six.py
index 0125d6b..4ca3200 100644
--- a/test_six.py
+++ b/test_six.py
@@ -389,6 +389,35 @@ def test_dictionary_iterators(monkeypatch):
         monkeypatch.undo()
 
 
+def test_dictionary_views(monkeypatch):
+    if sys.version_info[:2] <= (2, 6):
+        py.test.skip("view methods on dictionaries only available on 2.7+")
+    def stock_method_name(viewwhat):
+        """Given a method suffix like "keys" or "values", return the name
+        of the dict method that delivers those on the version of Python
+        we're running in."""
+        if six.PY3:
+            return viewwhat
+        return 'view' + viewwhat
+
+    class MyDict(dict):
+        pass
+
+    d = MyDict(zip(range(10), reversed(range(10))))
+    for name in "keys", "values", "items":
+        meth = getattr(six, "view" + name)
+        view = meth(d)
+        assert set(view) == set(getattr(d, name)())
+        record = []
+        def with_kw(*args, **kw):
+            record.append(kw["kw"])
+            return old(*args)
+        old = getattr(MyDict, stock_method_name(name))
+        monkeypatch.setattr(MyDict, stock_method_name(name), with_kw)
+        meth(d, kw=42)
+        assert record == [42]
+        monkeypatch.undo()
+
 def test_advance_iterator():
     assert six.next is six.advance_iterator
     l = [1, 2]