unicode_literals doesn't work in exec

[benjaminp]

BPO	4225
Nosy	@birkenfeld, @amauryfa, @benjaminp
PRs	bpo-42258: argparse: show choices once per argument #23143
Files	fix_exec_literals.patch pass_flags.patch parser_module_fixed_too.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2008-10-31.02:16:41.120>
created_at = <Date 2008-10-28.22:06:43.407>
labels = ['interpreter-core']
title = "unicode_literals doesn't work in exec"
updated_at = <Date 2020-11-04.11:39:21.453>
user = 'https://github.com/benjaminp'

bugs.python.org fields:

activity = <Date 2020-11-04.11:39:21.453>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2008-10-31.02:16:41.120>
closer = 'benjamin.peterson'
components = ['Interpreter Core']
creation = <Date 2008-10-28.22:06:43.407>
creator = 'benjamin.peterson'
dependencies = []
files = ['11903', '11906', '11912']
hgrepos = []
issue_num = 4225
keywords = ['patch', 'needs review']
message_count = 8.0
messages = ['75307', '75312', '75332', '75333', '75389', '75399', '75406', '75429']
nosy_count = 4.0
nosy_names = ['georg.brandl', 'amaury.forgeotdarc', 'benjamin.peterson', 'python-dev']
pr_nums = ['23143']
priority = 'high'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue4225'
versions = ['Python 2.6', 'Python 2.7']

[benjaminp]

exec "from __future__ import unicode_literals; print type('')"

gives <type 'str'> in 2.6/2.7. It's the result of flags not being passed
from the parser to AST.

[amauryfa]

The attached patch works, but can be simplified by using a stack variable:

Index: pythonrun.c
===================================================================
--- pythonrun.c (revision 66902)
+++ pythonrun.c (working copy)
@@ -1284,7 +1290,13 @@

 {
 	PyObject *ret = NULL;
 	mod_ty mod;
-	PyArena *arena = PyArena_New();
+	PyCompilerFlags localflags;
+	PyArena *arena;
+
+	if (flags == NULL)
+		flags = &localflags;
+
+	arena = PyArena_New();
 	if (arena == NULL)
 		return NULL;

[benjaminp]

This patch uses heap variables and tries to catch more places.

[amauryfa]

The newer patch is good.

I found another use of PyAST_FromNode() with NULL flags, and which has
the same problem:

import parser
s=parser.suite(
     "from __future__ import unicode_literals; print type('')")
eval(s.compile())

But I don't know how to correct this: the CO_FUTURE_UNICODE_LITERALS
flag is determined during the parse phase (in parser.suite), but this
value is lost and not passed to s.compile().
Maybe PyST_Object could grow a "st_flags" attribute.

[benjaminp]

Here's a patch that handles the parser module.

[amauryfa]

The patch is good,
except that you removed "static" before the function err_input (?)

[benjaminp]

The removal of the "static" was a mistake. Fixed in r67066.

[benjaminp]

This problem will still persist for anybody who uses PyParser_* APIs and
then PyNode_Compile, but we can probably only document that.