[Python-Dev] 'fast locals' in Python 2.5 (original) (raw)

Armin Rigo arigo at tunes.org
Wed Jun 7 10:39:41 CEST 2006

Hi,

On Wed, Jun 07, 2006 at 02:07:48AM +0200, Thomas Wouters wrote:

I just submitted http://python.org/sf/1501934 and assigned it to Neal so it doesn't get forgotten before 2.5 goes out ;) It seems Python 2.5 compiles the following code incorrectly:

No, no, it's an underground move by Jeremy to allow assignment to variables of enclosing scopes:

[in 2.5]
def f():
    x = 5
    def g():
        x += 1
    g()
    print x     # 6

The next move is to say that this is an expected feature of the augmented assignment operators, from which it follows naturally that we need a pseudo-augmented assignment that doesn't actually read the old value:

[in 2.6]
def f():
    x = 5
    def g():
        x := 6
    g()
    print x    # 6

Credits to Samuele's evil side for the ideas. His non-evil side doesn't agree, and neither does mine, of course :-)

More seriously, a function with a variable that is only written to as the target of augmented assignments cannot possibly be something else than a newcomer's mistake: the augmented assignments will always raise UnboundLocalError. Maybe this should be a SyntaxWarning?

A bientot,

Armin

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