[multi-db] Merge trunk to [3875]. Some tests still failing.

git-svn-id: http://code.djangoproject.com/svn/django/branches/multiple-db-support@4151 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 31 insertions, 0 deletions

diff --git a/django/utils/itercompat.py b/django/utils/itercompat.py
new file mode 100644
index 0000000000..370988bedb
--- /dev/null
+++ b/django/utils/itercompat.py
@@ -0,0 +1,31 @@
+"""
+Providing iterator functions that are not in all version of Python we support.
+Where possible, we try to use the system-native version and only fall back to
+these implementations if necessary.
+"""
+
+import itertools
+
+def compat_tee(iterable):
+    """Return two independent iterators from a single iterable.
+
+    Based on http://www.python.org/doc/2.3.5/lib/itertools-example.html
+    """
+    # Note: Using a dictionary and a list as the default arguments here is
+    # deliberate and safe in this instance.
+    def gen(next, data={}, cnt=[0]):
+        dpop = data.pop
+        for i in itertools.count():
+            if i == cnt[0]:
+                item = data[i] = next()
+                cnt[0] += 1
+            else:
+                item = dpop(i)
+            yield item
+    next = iter(iterable).next
+    return gen(next), gen(next)
+
+if hasattr(itertools, 'tee'):
+    tee = itertools.tee
+else:
+    tee = compat_tee