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Ned Deily3a2883c2019-06-12 23:31:45 -04001****************************
2 What's New In Python 3.9
3****************************
4
5:Release: |release|
6:Date: |today|
7
8.. Rules for maintenance:
9
10 * Anyone can add text to this document. Do not spend very much time
11 on the wording of your changes, because your text will probably
12 get rewritten to some degree.
13
14 * The maintainer will go through Misc/NEWS periodically and add
15 changes; it's therefore more important to add your changes to
16 Misc/NEWS than to this file.
17
18 * This is not a complete list of every single change; completeness
19 is the purpose of Misc/NEWS. Some changes I consider too small
20 or esoteric to include. If such a change is added to the text,
21 I'll just remove it. (This is another reason you shouldn't spend
22 too much time on writing your addition.)
23
24 * If you want to draw your new text to the attention of the
25 maintainer, add 'XXX' to the beginning of the paragraph or
26 section.
27
28 * It's OK to just add a fragmentary note about a change. For
29 example: "XXX Describe the transmogrify() function added to the
30 socket module." The maintainer will research the change and
31 write the necessary text.
32
33 * You can comment out your additions if you like, but it's not
34 necessary (especially when a final release is some months away).
35
36 * Credit the author of a patch or bugfix. Just the name is
37 sufficient; the e-mail address isn't necessary.
38
39 * It's helpful to add the bug/patch number as a comment:
40
41 XXX Describe the transmogrify() function added to the socket
42 module.
43 (Contributed by P.Y. Developer in :issue:`12345`.)
44
45 This saves the maintainer the effort of going through the Mercurial log
46 when researching a change.
47
48This article explains the new features in Python 3.9, compared to 3.8.
49
50For full details, see the :source:`Misc/NEWS` file.
51
52.. note::
53
54 Prerelease users should be aware that this document is currently in draft
55 form. It will be updated substantially as Python 3.9 moves towards release,
56 so it's worth checking back even after reading earlier versions.
57
58
59Summary -- Release highlights
60=============================
61
62.. This section singles out the most important changes in Python 3.9.
63 Brevity is key.
64
65
66.. PEP-sized items next.
67
68
69
70New Features
71============
72
73
74
75Other Language Changes
76======================
77
78
79
80New Modules
81===========
82
83* None yet.
84
85
86Improved Modules
87================
88
Victor Stinner066e5b12019-06-14 18:55:22 +020089threading
90---------
91
92In a subinterpreter, spawning a daemon thread now raises an exception. Daemon
93threads were never supported in subinterpreters. Previously, the subinterpreter
94finalization crashed with a Pyton fatal error if a daemon thread was still
95running.
96
Ned Deily3a2883c2019-06-12 23:31:45 -040097
98Optimizations
99=============
100
101
102Build and C API Changes
103=======================
104
Victor Stinner2ff58a22019-06-17 14:27:23 +0200105* Add a new public :c:func:`PyObject_CallNoArgs` function to the C API:
Victor Stinner5352cc42019-06-17 17:15:36 +0200106 call a callable Python object without any arguments. It is the most efficient
107 way to call a callable Python object without any argument.
108 (Contributed by Victor Stinner in :issue:`37194`.)
109
Ned Deily3a2883c2019-06-12 23:31:45 -0400110
111
112Deprecated
113==========
114
Serhiy Storchaka231aad32019-06-17 16:57:27 +0300115* Currently :func:`math.factorial` accepts :class:`float` instances with
116 non-negative integer values (like ``5.0``). It raises a :exc:`ValueError`
117 for non-integral and negative floats. It is deprecated now. In future
118 Python versions it will raise a :exc:`TypeError` for all floats.
119 (Contributed by Serhiy Storchaka in :issue:`37315`.)
Ned Deily3a2883c2019-06-12 23:31:45 -0400120
121
122Removed
123=======
124
Victor Stinner36456df2019-06-25 03:01:08 +0200125* The ``sys.getcheckinterval()`` and ``sys.setcheckinterval()`` functions have
126 been removed. They were deprecated since Python 3.2. Use
127 :func:`sys.getswitchinterval` and :func:`sys.setswitchinterval` instead.
128 (Contributed by Victor Stinner in :issue:`37392`.)
129
Victor Stinner987a0dc2019-06-19 10:36:10 +0200130* The C function ``PyImport_Cleanup()`` has been removed. It was documented as:
131 "Empty the module table. For internal use only."
Victor Stinnerc68e3fb2019-06-20 22:41:25 +0200132 (Contributed by Victor Stinner in :issue:`36710`.)
Victor Stinner987a0dc2019-06-19 10:36:10 +0200133
Victor Stinnerac7b1a32019-06-18 00:00:24 +0200134* ``_dummy_thread`` and ``dummy_threading`` modules have been removed. These
135 modules were deprecated since Python 3.7 which requires threading support.
136 (Contributed by Victor Stinner in :issue:`37312`.)
137
138* ``aifc.openfp()`` alias to ``aifc.open()``, ``sunau.openfp()`` alias to
139 ``sunau.open()``, and ``wave.openfp()`` alias to ``wave.open()`` have been
140 removed. They were deprecated since Python 3.7.
141 (Contributed by Victor Stinner in :issue:`37320`.)
Ned Deily3a2883c2019-06-12 23:31:45 -0400142
143
144Porting to Python 3.9
145=====================
146
147This section lists previously described changes and other bugfixes
148that may require changes to your code.
149
150