bpo-36320: Switch typing.NamedTuple from OrderedDict to regular dict (GH-12396)
Also, deprecate the *_field_types* attributes which duplicated the information in *\__annotations__*.
https://bugs.python.org/issue36320
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
index de03284..fad9dc6 100644
--- a/Doc/library/typing.rst
+++ b/Doc/library/typing.rst
@@ -838,10 +838,11 @@
Fields with a default value must come after any fields without a default.
- The resulting class has two extra attributes: ``_field_types``,
- giving a dict mapping field names to types, and ``_field_defaults``, a dict
- mapping field names to default values. (The field names are in the
- ``_fields`` attribute, which is part of the namedtuple API.)
+ The resulting class has an extra attribute ``__annotations__`` giving a
+ dict that maps the field names to the field types. (The field names are in
+ the ``_fields`` attribute and the default values are in the
+ ``_field_defaults`` attribute both of which are part of the namedtuple
+ API.)
``NamedTuple`` subclasses can also have docstrings and methods::
@@ -863,6 +864,15 @@
.. versionchanged:: 3.6.1
Added support for default values, methods, and docstrings.
+ .. versionchanged:: 3.8
+ Deprecated the ``_field_types`` attribute in favor of the more
+ standard ``__annotations__`` attribute which has the same information.
+
+ .. versionchanged:: 3.8
+ The ``_field_types`` and ``__annotations__`` attributes are
+ now regular dictionaries instead of instances of ``OrderedDict``.
+
+
.. function:: NewType(typ)
A helper function to indicate a distinct types to a typechecker,
diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index 31baccd..2e311ab 100644
--- a/Doc/whatsnew/3.8.rst
+++ b/Doc/whatsnew/3.8.rst
@@ -510,6 +510,10 @@
(Contributed by Berker Peksag in :issue:`9372`.)
+* The :class:`typing.NamedTuple` class has deprecated the ``_field_types``
+ attribute in favor of the ``__annotations__`` attribute which has the same
+ information. (Contributed by Raymond Hettinger in :issue:`36320`.)
+
* :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and
``Ellipsis`` are considered deprecated and will be removed in future Python
versions. :class:`~ast.Constant` should be used instead.
diff --git a/Lib/typing.py b/Lib/typing.py
index 3243e2a..530d463 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1325,8 +1325,8 @@
types = [(n, _type_check(t, msg)) for n, t in types]
nm_tpl = collections.namedtuple(name, [n for n, t in types])
# Prior to PEP 526, only _field_types attribute was assigned.
- # Now, both __annotations__ and _field_types are used to maintain compatibility.
- nm_tpl.__annotations__ = nm_tpl._field_types = collections.OrderedDict(types)
+ # Now __annotations__ are used and _field_types is deprecated (remove in 3.9)
+ nm_tpl.__annotations__ = nm_tpl._field_types = dict(types)
try:
nm_tpl.__module__ = sys._getframe(2).f_globals.get('__name__', '__main__')
except (AttributeError, ValueError):
@@ -1361,7 +1361,7 @@
"follow default field(s) {default_names}"
.format(field_name=field_name,
default_names=', '.join(defaults_dict.keys())))
- nm_tpl.__new__.__annotations__ = collections.OrderedDict(types)
+ nm_tpl.__new__.__annotations__ = dict(types)
nm_tpl.__new__.__defaults__ = tuple(defaults)
nm_tpl._field_defaults = defaults_dict
# update from user namespace without overriding special namedtuple attributes
@@ -1386,12 +1386,10 @@
Employee = collections.namedtuple('Employee', ['name', 'id'])
- The resulting class has extra __annotations__ and _field_types
- attributes, giving an ordered dict mapping field names to types.
- __annotations__ should be preferred, while _field_types
- is kept to maintain pre PEP 526 compatibility. (The field names
- are in the _fields attribute, which is part of the namedtuple
- API.) Alternative equivalent keyword syntax is also accepted::
+ The resulting class has an extra __annotations__ attribute, giving a
+ dict that maps field names to types. (The field names are also in
+ the _fields attribute, which is part of the namedtuple API.)
+ Alternative equivalent keyword syntax is also accepted::
Employee = NamedTuple('Employee', name=str, id=int)
diff --git a/Misc/NEWS.d/next/Library/2019-03-18-01-08-14.bpo-36320.-06b9_.rst b/Misc/NEWS.d/next/Library/2019-03-18-01-08-14.bpo-36320.-06b9_.rst
new file mode 100644
index 0000000..9e9495f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-03-18-01-08-14.bpo-36320.-06b9_.rst
@@ -0,0 +1,3 @@
+The typing.NamedTuple() class has deprecated the _field_types attribute in
+favor of the __annotations__ attribute which carried the same information.
+Also, both attributes were converted from OrderedDict to a regular dict.