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bpo-35766: Change format for feature_version to (major, minor) #13992

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miss-islington merged 1 commit into from
Jun 12, 2019
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bpo-35766: Change format for feature_version to (major, minor) #13992

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13 changes: 7 additions & 6 deletions Doc/library/ast.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -126,7 +126,7 @@ The abstract grammar is currently defined as follows:
Apart from the node classes, the :mod:`ast` module defines these utility functions
and classes for traversing abstract syntax trees:

.. function:: parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=-1)
.. function:: parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=None)

Parse the source into an AST node. Equivalent to ``compile(source,
filename, mode, ast.PyCF_ONLY_AST)``.
Expand All @@ -145,11 +145,12 @@ and classes for traversing abstract syntax trees:
modified to correspond to :pep:`484` "signature type comments",
e.g. ``(str, int) -> List[str]``.

Also, setting ``feature_version`` to the minor version of an
earlier Python 3 version will attempt to parse using that version's
grammar. For example, setting ``feature_version=4`` will allow
the use of ``async`` and ``await`` as variable names. The lowest
supported value is 4; the highest is ``sys.version_info[1]``.
Also, setting ``feature_version`` to a tuple ``(major, minor)``
will attempt to parse using that Python version's grammar.
Currently ``major`` must equal to ``3``. For example, setting
``feature_version=(3, 4)`` will allow the use of ``async`` and
``await`` as variable names. The lowest supported version is
``(3, 4)``; the highest is ``sys.version_info[0:2]``.
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@gvanrossum gvanrossum Jun 11, 2019

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Note that there's a subtle difference between "must equal to 3" (the call fails if it isn't) and "supported" -- versions outside the supported range are treated as the lowest or highest supported version, respectively.


.. warning::
It is possible to crash the Python interpreter with a
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6 changes: 3 additions & 3 deletions Doc/whatsnew/3.8.rst
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Expand Up @@ -378,9 +378,9 @@ The :func:`ast.parse` function has some new flags:
* ``mode='func_type'`` can be used to parse :pep:`484` "signature type
comments" (returned for function definition AST nodes);

* ``feature_version=N`` allows specifying the minor version of an
earlier Python 3 version. (For example, ``feature_version=4`` will
treat ``async`` and ``await`` as non-reserved words.)
* ``feature_version=(3, N)`` allows specifying an earlier Python 3
version. (For example, ``feature_version=(3, 4)`` will treat
``async`` and ``await`` as non-reserved words.)

New function :func:`ast.get_source_segment` returns the source code
for a specific AST node.
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9 changes: 8 additions & 1 deletion Lib/ast.py
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Expand Up @@ -28,7 +28,7 @@


def parse(source, filename='<unknown>', mode='exec', *,
type_comments=False, feature_version=-1):
type_comments=False, feature_version=None):
"""
Parse the source into an AST node.
Equivalent to compile(source, filename, mode, PyCF_ONLY_AST).
Expand All @@ -37,6 +37,13 @@ def parse(source, filename='<unknown>', mode='exec', *,
flags = PyCF_ONLY_AST
if type_comments:
flags |= PyCF_TYPE_COMMENTS
if isinstance(feature_version, tuple):
major, minor = feature_version # Should be a 2-tuple.
assert major == 3
feature_version = minor
elif feature_version is None:
feature_version = -1
# Else it should be an int giving the minor version for 3.x.
return compile(source, filename, mode, flags,
feature_version=feature_version)
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@vstinner vstinner Jun 11, 2019

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Oh. I didn't notice that that compile() has a feature_version parameter as well. If if's only used by AST and should not be used explicitly, would it make sense to rename it to _feature_version in compile()? By the way, maybe it would be better to declare the feature_version/_feature_version parameter as a keyword-only to avoid mistakes.

In short, I suggest this change (+ run "make clinic"):

diff --git a/Lib/ast.py b/Lib/ast.py
index 64e7a2551f..02ad8df81f 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -38,7 +38,7 @@ def parse(source, filename='<unknown>', mode='exec', *,
     if type_comments:
         flags |= PyCF_TYPE_COMMENTS
     return compile(source, filename, mode, flags,
-                   feature_version=feature_version)
+                   _feature_version=feature_version)
 
 
 def literal_eval(node_or_string):
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 56d882d387..abf807a408 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -696,7 +696,8 @@ compile as builtin_compile
     flags: int = 0
     dont_inherit: bool(accept={int}) = False
     optimize: int = -1
-    feature_version: int = -1
+    *
+    _feature_version as feature_version: int = -1
 
 Compile source into a code object that can be executed by exec() or eval().


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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2019-06-11-16-41-40.bpo-35766.v1Kj-T.rst
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@@ -0,0 +1 @@
Change the format of feature_version to be a (major, minor) tuple.