[New-bugs-announce] [issue14378] __future__ imports fail when compiling from python ast

[J. D. Bartlett]

New submission from J. D. Bartlett <josh at bartletts.id.au>:

GOAL
I am trying to compile an AST which contains an ImportFrom node which performs a __future__ import. The ImportFrom node in question is the first node within the AST's body (as it should be, because __future__ imports must occur at the beginning of modules).

ISSUE
Compiling the AST fails with the error "SyntaxError: from __future__ imports must occur at the beginning of the file".

ANALYSIS
The future_parse() function in future.c looks for __future__ imports and identifies them based on the condition (ds->v.ImportFrom.module == future) where future is constructed using PyString_InternFromString("__future__"). That is, the module attribute of the ImportFrom node is compared by identity with the interned string "__future__".

The AST which I was compiling used the string "__future__" after extracting that string from a much longer string of user input, and as a result, the string was not interned.

The attached file futureimport.py is a simple script demonstrating this issue. I have confirmed that the issue occurs in Python 2.7.2 and 3.2.2.

----------
components: Interpreter Core
files: futureimport.py
messages: 156477
nosy: talljosh
priority: normal
severity: normal
status: open
title: __future__ imports fail when compiling from python ast
type: behavior
versions: Python 2.7, Python 3.2
Added file: http://bugs.python.org/file24981/futureimport.py

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue14378>
_______________________________________