[issue4381] Cannot declare multiple classes via exec when inside a function.

2008-11-21 Thread Kevin Fitch 

New submission from Kevin Fitch [EMAIL PROTECTED]:

codeText = 
class foo(object): pass
class bar(object):
  baz = foo()


def doExec(text):
  exec text

### This works:
# Although if I do this before the doExec below, then the
# doExec doesn't fail.
# exec codeText

### But this does not:
doExec(codeText)


The output I get is:
---
type 'exceptions.NameError' Traceback (most recent call last)

/home/kfitch/ipython console in module()

/home/kfitch/ipython console in doExec(text)

/home/kfitch/string in module()

/home/kfitch/string in bar()

type 'exceptions.NameError': name 'foo' is not defined



I don't fully understand why the version in the function doesn't work,
but I suspect it is a bug related to scoping, since foo is really
doExec.foo (I think).

This is with python 2.5.2 under Linux (Ubuntu 8.04)

--
messages: 76202
nosy: kfitch
severity: normal
status: open
title: Cannot declare multiple classes via exec when inside a function.
versions: Python 2.5

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[issue4381] Cannot declare multiple classes via exec when inside a function.

2008-11-21 Thread Amaury Forgeot d'Arc 

Amaury Forgeot d'Arc [EMAIL PROTECTED] added the comment:

I agree that it is confusing; in short: a bare exec() does not play well with 
closures;  
This is a consequence of the python execution model, and is unlikely to change.

Here, the class 'foo' is stored in the function's local variables.
But the execution of the body of the 'bar' class searches names in its local 
scope (the 
class body) and the global scope (the module level), and misses the function's 
locals...

I strongly suggest to avoid pure exec() statements; always specify a global 
and/or a 
local dictionary.

In your case, the following works:

def doExec(text):
  d = {}  # or:   d = dict(globals())
  exec text in d
  print d.keys()

--
nosy: +amaury.forgeotdarc
resolution:  - wont fix
status: open - closed

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