Added documentation for Length class.

BTrees/Length.py

@@ -43,13 +43,16 @@ class Length(persistent.Persistent):
         self.value = v
 
     def set(self, v):
+        "Set the length value to v."
         self.value = v
 
     def _p_resolveConflict(self, old, s1, s2):
         return s1 + s2 - old
 
     def change(self, delta):
+        "Add delta to the length value."
         self.value += delta
 
     def __call__(self, *args):
+        "Return the current length value."
         return self.value

docs/api.rst

@@ -96,3 +96,13 @@ Protocol APIs
   .. autointerface:: IIntegerFloatBTreeModule
      :members:
      :member-order: bysource
+
+Utilities
+-------------
+
+.. automodule:: BTrees.Length
+
+  .. autoclass:: Length
+     :members:
+
+     .. automethod:: __call__