[pypy-svn] r32558 - pypy/dist/pypy/annotation

[arigo at codespeak.net]

Author: arigo
Date: Thu Sep 21 11:34:49 2006
New Revision: 32558

Modified:
   pypy/dist/pypy/annotation/pairtype.py
Log:
Added docstring.


Modified: pypy/dist/pypy/annotation/pairtype.py
==============================================================================
--- pypy/dist/pypy/annotation/pairtype.py	(original)
+++ pypy/dist/pypy/annotation/pairtype.py	Thu Sep 21 11:34:49 2006
@@ -1,5 +1,30 @@
 """
-XXX A docstring should go here.
+Two magic tricks for classes:
+
+    class X:
+        __metaclass__ = extendabletype
+        ...
+
+    # in some other file...
+    class __extend__(X):
+        ...      # and here you can add new methods and class attributes to X
+
+Mostly useful together with the second trick, which lets you build
+methods whose 'self' is a pair of objects instead of just one:
+
+    class __extend__(pairtype(X, Y)):
+        attribute = 42
+        def method((x, y), other, arguments):
+            ...
+
+    pair(x, y).attribute
+    pair(x, y).method(other, arguments)
+
+This finds methods and class attributes based on the actual
+class of both objects that go into the pair(), with the usual
+rules of method/attribute overriding in (pairs of) subclasses.
+
+For more information, see test_pairtype.
 """
 
 class extendabletype(type):