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@@ -179,6 +179,57 @@ a normal ``__getattr__`` method, except that it will be defined on module
PEP written and implemented by Ivan Levkivskyi
+PEP 563: Postponed evaluation of annotations
+--------------------------------------------
+
+The advent of type hints in Python uncovered two glaring usability issues
+with the functionality of annotations added in :pep:`3107` and refined
+further in :pep:`526`:
+
+* annotations could only use names which were already available in the
+ current scope, in other words they didn't support forward references
+ of any kind; and
+
+* annotating source code had adverse effects on startup time of Python
+ programs.
+
+Both of these issues are fixed by postponing the evaluation of
+annotations. Instead of compiling code which executes expressions in
+annotations at their definition time, the compiler stores the annotation
+in a string form equivalent to the AST of the expression in question.
+If needed, annotations can be resolved at runtime using
+``typing.get_type_hints()``. In the common case where this is not
+required, the annotations are cheaper to store (since short strings
+are interned by the interpreter) and make startup time faster.
+
+Usability-wise, annotations now support forward references, making the
+following syntax valid::
+
+ class C:
+ @classmethod
+ def from_string(cls, source: str) -> C:
+ ...
+
+ def validate_b(self, obj: B) -> bool:
+ ...
+
+ class B:
+ ...
+
+Since this change breaks compatibility, the new behavior can be enabled
+on a per-module basis in Python 3.7 using a ``__future__`` import, like
+this::
+
+ from __future__ import annotations
+
+It will become the default in Python 4.0.
+
+.. seealso::
+
+ :pep:`563` -- Postponed evaluation of annotations
+ PEP written and implemented by Ɓukasz Langa.
+
+
PEP 564: Add new time functions with nanosecond resolution
----------------------------------------------------------