List of changes from previous release in the ASDL.

python 2.6
-----------

 * `ClassDef`: added field `decorator_list`
 * `excepthandler`: added attributes


python 2.7
------------

 * `ImportFrom`: field `module` became optional
 * `expr`: definition added types `Set`, `SetComp`, `DictComp`


python 3.0
------------

 * removed builtin type `bool`
 * `FunctionDef`: added field `returns`
 * `ClassDef`: added fields `keywords`, `startargs`, `kwargs`
 * `stmt` definition: removed `Print`
 * `Raise`: fields where changed to `exc` and `cause`
 * `ImportFrom`: field `module` became required
 * `stmt` definition: removed `Exec`
 * `stmt` definition: added `Nonlocal`
 * `expr` definition: remove `Repr`
 * `expr` definition: added `Bytes`
 * `expr` definition: added `Ellipsis`
 * `expr` definition: added `Starred`
 * `slice` definition: removed `Ellipsis`
 * `ExceptHandler`: field `identifier`'s type changed from `expr` to `identifier`
 * `arguments`: changed fields
 * added definition `arg`


python 3.1
------------

(no changes)


python 3.2
------------

 * `ImportFrom`: field `module` became optional


python 3.3
------------

 * added builtin `bytes`
 * `With`: replace field `context_expr` and `option_vars` with `items`
 * added definition for `withitem`
 * `stmt` definition: replaced `TryExcept` and `TryFinally` with `Try`
 * `expr` definition: added `YieldFrom`
 * `Bytes` field `s`: changed type from `string` to `bytes`


python 3.4
-----------

 * added builtin `singleton`
 * `expr` definition: added NameConstant
 * `arguments` definition: fields changes
 * `arg` definition: added attributes
