add athing in adict

[Imported from Trac: page CodingStandards, version 30]

CodingStandards.md

@@ -43,6 +43,10 @@ from allmydata.util.assertutil import _assert, precondition, postcondition
  * Don't use the literals `True` or `False` in conditional expressions -- instead just write the expression which will evaluate to true or false. For example, write `if expr:` instead of `if expr == True:` and `if not expr:` instead of `if expr == False:`.
  * Avoid relying on the fact that empty sequences, empty strings, empty dicts, `0`, and `None` are treated as false. Write `if len(items) == 0:`, `if thing is None:`, etc.
 
+### Miscellaneous
+
+ * `athing in adict.keys()` can be replaced by `athing in adict`, which evaluates to the same boolean result, but is more succinct and more efficient at run-time.
+
 ## Idioms
 
 ### Preconditions and Assertions
@@ -164,8 +168,6 @@ class BlockStore:
         self.maintainertype = maintainertype
         self.backendtype = backendtype
 ```
-.
-
 
 ## Official Python Standards