bpo-38605: Revert making 'from __future__ import annotations' the def…

…ault (GH-25490) This reverts commits 044a104 and 1be456a, adapting the code to changes that happened after it.
python · Apr 21, 2021 · b0544ba77cf86074fb1adde00558c67ca75eeea1 · b0544ba
1 parent d35eef3
commit b0544ba77cf86074fb1adde00558c67ca75eeea1
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
@@ -1244,9 +1244,13 @@ following the parameter name.  Any parameter may have an annotation, even those
 ``*identifier`` or ``**identifier``.  Functions may have "return" annotation of
 the form "``-> expression``" after the parameter list.  These annotations can be
 any valid Python expression.  The presence of annotations does not change the
-semantics of a function.  The annotation values are available as string values
-in a dictionary keyed by the parameters' names in the :attr:`__annotations__`
-attribute of the function object.
+semantics of a function.  The annotation values are available as values of
+a dictionary keyed by the parameters' names in the :attr:`__annotations__`
+attribute of the function object.  If the ``annotations`` import from
+:mod:`__future__` is used, annotations are preserved as strings at runtime which
+enables postponed evaluation.  Otherwise, they are evaluated when the function
+definition is executed.  In this case annotations may be evaluated in
+a different order than they appear in the source code.
 
 .. index:: pair: lambda; expression
 

diff --git a/Doc/reference/simple_stmts.rst b/Doc/reference/simple_stmts.rst
@@ -877,11 +877,14 @@ can appear before a future statement are:
 * blank lines, and
 * other future statements.
 
+The only feature that requires using the future statement is
+``annotations`` (see :pep:`563`).
+
 All historical features enabled by the future statement are still recognized
 by Python 3.  The list includes ``absolute_import``, ``division``,
 ``generators``, ``generator_stop``, ``unicode_literals``,
-``print_function``, ``nested_scopes``, ``with_statement`` and ``annotations``.
-They are all redundant because they are always enabled, and only kept for
+``print_function``, ``nested_scopes`` and ``with_statement``.  They are
+all redundant because they are always enabled, and only kept for
 backwards compatibility.
 
 A future statement is recognized and treated specially at compile time: Changes

diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
@@ -624,22 +624,6 @@ This section covers major changes affecting :pep:`484` type annotations and
 the :mod:`typing` module.
 
 
-PEP 563: Postponed Evaluation of Annotations Becomes Default
-------------------------------------------------------------
-
-In Python 3.7, postponed evaluation of annotations was added,
-to be enabled with a ``from __future__ import annotations``
-directive.  In 3.10 this became the default behavior, even
-without that future directive.  With this being default, all
-annotations stored in :attr:`__annotations__` will be strings.
-If needed, annotations can be resolved at runtime using
-:func:`typing.get_type_hints`.  See :pep:`563` for a full
-description.  Also, the :func:`inspect.signature` will try to
-resolve types from now on, and when it fails it will fall back to
-showing the string annotations.  (Contributed by Batuhan Taskaya
-in :issue:`38605`.)
-
-
 PEP 604: New Type Union Operator
 --------------------------------
 

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
@@ -413,10 +413,8 @@ def _create_fn(name, args, body, *, globals=None, locals=None,
 
     ns = {}
     exec(txt, globals, ns)
-    func = ns['__create_fn__'](**locals)
-    for arg, annotation in func.__annotations__.copy().items():
-        func.__annotations__[arg] = locals[annotation]
-    return func
+    return ns['__create_fn__'](**locals)
+
 
 def _field_assign(frozen, name, value, self_name):
     # If we're a frozen class, then assign to our fields in __init__
@@ -667,11 +665,6 @@ def _is_type(annotation, cls, a_module, a_type, is_type_predicate):
     # a eval() penalty for every single field of every dataclass
     # that's defined.  It was judged not worth it.
 
-    # Strip away the extra quotes as a result of double-stringifying when the
-    # 'annotations' feature became default.
-    if annotation.startswith(("'", '"')) and annotation.endswith(("'", '"')):
-        annotation = annotation[1:-1]
-
     match = _MODULE_IDENTIFIER_RE.match(annotation)
     if match:
         ns = None
@@ -1020,7 +1013,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
     if not getattr(cls, '__doc__'):
         # Create a class doc-string.
         cls.__doc__ = (cls.__name__ +
-                       str(inspect.signature(cls)).replace(' -> NoneType', ''))
+                       str(inspect.signature(cls)).replace(' -> None', ''))
 
     if match_args:
         _set_new_attribute(cls, '__match_args__',

diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
@@ -349,6 +349,7 @@ def _write_atomic(path, data, mode=0o666):
 #     Python 3.10a6 3434 (PEP 634: Structural Pattern Matching)
 #     Python 3.10a7 3435 Use instruction offsets (as opposed to byte offsets).
 #     Python 3.10b1 3436 (Add GEN_START bytecode #43683)
+#     Python 3.10b1 3437 (Undo making 'annotations' future by default - We like to dance among core devs!)
 
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
@@ -358,7 +359,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3436).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3437).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'

diff --git a/Lib/inspect.py b/Lib/inspect.py
@@ -45,7 +45,6 @@
 import tokenize
 import token
 import types
-import typing
 import warnings
 import functools
 import builtins
@@ -1893,10 +1892,7 @@ def _signature_is_functionlike(obj):
     code = getattr(obj, '__code__', None)
     defaults = getattr(obj, '__defaults__', _void) # Important to use _void ...
     kwdefaults = getattr(obj, '__kwdefaults__', _void) # ... and not None here
-    try:
-        annotations = _get_type_hints(obj)
-    except AttributeError:
-        annotations = None
+    annotations = getattr(obj, '__annotations__', None)
 
     return (isinstance(code, types.CodeType) and
             isinstance(name, str) and
@@ -2137,16 +2133,6 @@ def p(name_node, default_node, default=empty):
 
     return cls(parameters, return_annotation=cls.empty)
 
-def _get_type_hints(func, **kwargs):
-    try:
-        return typing.get_type_hints(func, **kwargs)
-    except Exception:
-        # First, try to use the get_type_hints to resolve
-        # annotations. But for keeping the behavior intact
-        # if there was a problem with that (like the namespace
-        # can't resolve some annotation) continue to use
-        # string annotations
-        return func.__annotations__
 
 def _signature_from_builtin(cls, func, skip_bound_arg=True):
     """Private helper function to get signature for
@@ -2191,8 +2177,7 @@ def _signature_from_function(cls, func, skip_bound_arg=True,
     positional = arg_names[:pos_count]
     keyword_only_count = func_code.co_kwonlyargcount
     keyword_only = arg_names[pos_count:pos_count + keyword_only_count]
-    annotations = _get_type_hints(func, globalns=globalns, localns=localns)
-
+    annotations = func.__annotations__
     defaults = func.__defaults__
     kwdefaults = func.__kwdefaults__
 

diff --git a/Lib/test/dataclass_module_1.py b/Lib/test/dataclass_module_1.py
@@ -1,3 +1,9 @@
+#from __future__ import annotations
+USING_STRINGS = False
+
+# dataclass_module_1.py and dataclass_module_1_str.py are identical
+# except only the latter uses string annotations.
+
 import dataclasses
 import typing
 

diff --git a/Lib/test/dataclass_module_1_str.py b/Lib/test/dataclass_module_1_str.py
@@ -0,0 +1,32 @@
+from __future__ import annotations
+USING_STRINGS = True
+
+# dataclass_module_1.py and dataclass_module_1_str.py are identical
+# except only the latter uses string annotations.
+
+import dataclasses
+import typing
+
+T_CV2 = typing.ClassVar[int]
+T_CV3 = typing.ClassVar
+
+T_IV2 = dataclasses.InitVar[int]
+T_IV3 = dataclasses.InitVar
+
+@dataclasses.dataclass
+class CV:
+    T_CV4 = typing.ClassVar
+    cv0: typing.ClassVar[int] = 20
+    cv1: typing.ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclasses.dataclass
+class IV:
+    T_IV4 = dataclasses.InitVar
+    iv0: dataclasses.InitVar[int]
+    iv1: dataclasses.InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/dataclass_module_2.py b/Lib/test/dataclass_module_2.py
@@ -1,3 +1,9 @@
+#from __future__ import annotations
+USING_STRINGS = False
+
+# dataclass_module_2.py and dataclass_module_2_str.py are identical
+# except only the latter uses string annotations.
+
 from dataclasses import dataclass, InitVar
 from typing import ClassVar
 

diff --git a/Lib/test/dataclass_module_2_str.py b/Lib/test/dataclass_module_2_str.py
@@ -0,0 +1,32 @@
+from __future__ import annotations
+USING_STRINGS = True
+
+# dataclass_module_2.py and dataclass_module_2_str.py are identical
+# except only the latter uses string annotations.
+
+from dataclasses import dataclass, InitVar
+from typing import ClassVar
+
+T_CV2 = ClassVar[int]
+T_CV3 = ClassVar
+
+T_IV2 = InitVar[int]
+T_IV3 = InitVar
+
+@dataclass
+class CV:
+    T_CV4 = ClassVar
+    cv0: ClassVar[int] = 20
+    cv1: ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclass
+class IV:
+    T_IV4 = InitVar
+    iv0: InitVar[int]
+    iv1: InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/dataclass_textanno.py b/Lib/test/dataclass_textanno.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import dataclasses