String annotations [PEP 563] (#4390)

* Document `from __future__ import annotations`
* Provide plumbing and tests for `from __future__ import annotations`
* Implement unparsing the AST back to string form

This is required for PEP 563 and as such only implements a part of the
unparsing process that covers expressions.

1 files changed, 10 insertions, 7 deletions

diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index f0fcb62..dcfe086 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -372,9 +372,11 @@ Glossary
       may be accessed via the :attr:`__annotations__` special attribute of a
       function object.
 
-      Python itself does not assign any particular meaning to function
-      annotations. They are intended to be interpreted by third-party libraries
-      or tools.  See :pep:`3107`, which describes some of their potential uses.
+      See also the :term:`variable annotation` glossary entry.
+
+      Annotations are meant to provide a standard way for programmers to
+      document types of functions they design.  See :pep:`484`, which
+      describes this functionality.
 
    __future__
       A pseudo-module which programmers can use to enable new language features
@@ -1021,10 +1023,11 @@ Glossary
       attribute of a class or module object and can be accessed using
       :func:`typing.get_type_hints`.
 
-      Python itself does not assign any particular meaning to variable
-      annotations. They are intended to be interpreted by third-party libraries
-      or type checking tools. See :pep:`526`, :pep:`484` which describe
-      some of their potential uses.
+      See also the :term:`function annotation` glossary entry.
+
+      Annotations are meant to provide a standard way for programmers to
+      document types of functions they design.  See :pep:`484` and :pep:`526`
+      which describe this functionality.
 
    virtual environment
       A cooperatively isolated runtime environment that allows Python users