execfile fixer produces code that does not close the file

[smarnach]

BPO	13332
Nosy	@pitrou, @benjaminp, @asmeurer, @akheron, @smarnach
Superseder	bpo-45544: Close 2to3 issues and list them here

^{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 2021-10-20.22:36:26.926>
created_at = <Date 2011-11-03.12:11:31.896>
labels = ['type-bug', 'expert-2to3']
title = 'execfile fixer produces code that does not close the file'
updated_at = <Date 2021-10-20.22:41:03.719>
user = 'https://github.com/smarnach'

bugs.python.org fields:

activity = <Date 2021-10-20.22:41:03.719>
actor = 'iritkatriel'
assignee = 'none'
closed = True
closed_date = <Date 2021-10-20.22:36:26.926>
closer = 'iritkatriel'
components = ['2to3 (2.x to 3.x conversion tool)']
creation = <Date 2011-11-03.12:11:31.896>
creator = 'smarnach'
dependencies = []
files = []
hgrepos = []
issue_num = 13332
keywords = []
message_count = 6.0
messages = ['146918', '146924', '146925', '146931', '146953', '146977']
nosy_count = 6.0
nosy_names = ['pitrou', 'benjamin.peterson', 'VPeric', 'Aaron.Meurer', 'petri.lehtinen', 'smarnach']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = '45544'
type = 'behavior'
url = 'https://bugs.python.org/issue13332'
versions = ['Python 3.2', 'Python 3.3']

[smarnach]

The execfile fixer of the 2to3 script replaces the 2.x code

    execfile("a.py")

by

exec(compile(open("a.py").read(), "a.py", 'exec'))

The new code does not explicitly close the file. This is not usually a problem in CPython, but

1. the code will throw a RessourceWarnings if enabled and

2. other Python implementation don't close the file immediately.

(I think the 2to3 script should be as implementation-independent as possible.)

The obvious fix would be to use a with-statement:

    with open("a.py") as new_name:
        exec(compile(new_name.read(), "a.py", 'exec'))

If this is to be changed, I'd be happy to prepare a patch.

[akheron]

Sounds reasonable to me. Is it easy to generate unique identifier names in 2to3 fixers?

[pitrou]

Be aware that execfile() is a simple function call and can be used in any expression.

[smarnach]

@petri: Yes, that's what the BaseFix.new_name() method is for.

@antoine: I thought about this, though I don't think it is very common to call execfile() as part of an expression. The whole statement containing the function call would need to be wrapped.

[smarnach]

Getting the general case right seems a bit too difficult. Examples like

[execfile(n) for n in names if condition(n)]

execfile(execfile(n1) or n2)

try: 1 / 0
except execfile(n) or ZeroDivisionError: pass

would require rather complex transformations to get exactly matching behaviour, and obviously we don't want to explode the fixer code to support such nonsense.

I think it is enough to cover the case of an execfile() call that forms a statement of its own. Browsing through the first ten pages of a Google code search for "execfile" didn't reveal any other uses, except for a few that aren't covered by the current version of the fixer either. 1

I'd suggest to simply throw a "could not convert" warning for any other uses of execfile(). Opinions?

[benjaminp]

Or you could just explicitly write out the exec(compile()) in your 2.x code.