On Wed, 26 Feb 2014 13:15:25 +0000, Steven D'Aprano wrote: > I have to dynamically generate some code inside a function using exec, > but I'm not sure if it is working by accident or if I can rely on it. > > Here is a trivial example: > > > py> def spam(): > ... exec( """x = 23""" ) > ... return x ... > py> spam() > 23 > > > (My real example is more complex than this.) > > According to the documentation of exec, I don't think this should > actually work, and yet it appears to. The documentation says: > > The default locals act as described for function locals() below: > modifications to the default locals dictionary should not be > attempted. Pass an explicit locals dictionary if you need to see > effects of the code on locals after function exec() returns. > > http://docs.python.org/3.4/library/functions.html#exec > > > I *think* this means that if I want to guarantee that a local variable x > is created by exec, I need to do this instead: > > py> def eggs(): > ... mylocals = {} > ... exec( """x = 23""", globals(), mylocals) > ... x = mylocals['x'] > ... return x ... > py> eggs() > 23 > > The fact that it works in spam() above is perhaps an accident of > implementation? Yes no maybe?
I have no idea but as exec is generally considered to be a bad idea are you absolutely sure this is the correct way to achieve your end goal? perhaps if you detailed your requirement someone may be able to suggest a safer solution. -- "Regardless of the legal speed limit, your Buick must be operated at speeds faster than 85 MPH (140kph)." -- 1987 Buick Grand National owners manual. -- https://mail.python.org/mailman/listinfo/python-list
