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.

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

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

@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.

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?

[1]: http://www.google.com/codesearch#yqvQ9RM69FY/mercurial/lsprof.py&q=execfile&sq=&l=111&ct=rc&cd=49

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