Exec woes

Hendrik van Rooyen mail at microcorp.co.za
Thu Jan 29 09:15:57 CET 2009


 "Rhodri James" <rhodri at wildebst.demon.co.uk> wrote:
To: <python-list at python.org>
Sent: Thursday, January 29, 2009 6:12 AM
Subject: Re: Exec woes


> On Wed, 28 Jan 2009 07:47:00 -0000, Hendrik van Rooyen
> <mail at mic,..p.co.za> wrote:

> > This is actually not correct - it is the root cause of my trouble.
> > if you write, in a nested scope:
> >
> > exec ( "somestring to execute" in globals(),locals())
> >
> > You get the syntax error, as the interpreter somehow sees it as one,
> > unqualified thing.
>
> Well, no.  Look at the error Python gives you, nested scope or not:
>
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> TypeError: exec: arg 1 must be a string, file, or code object
>
> If exec is a function, arg 1 is the boolean expression
>    "somestring to execute" in globals()
> which is unlikely to be what you want.  If exec is a statement,
> arg 1 is a tuple of two elements,
>    "somestring to execute" in globals()
> and
>    locals()
> which is also unlikely to be what you want.  Neither of these are
> giving you a string, file or code object, exactly as the interpreter
> is telling you.

Well, no - I stick by my assertion, about the nested scope:

>>> def rubbish():
 def deep_rubbish():
  exec('BUILD = "somestring"' in globals(),locals())

SyntaxError: unqualified exec is not allowed in function 'deep_rubbish' it is a
nested function (<pyshell#3>, line 3)
>>>

That is all I was saying - It was the brackets that buggered me,
and adding the globals() and locals() inside the brackets, inside
the nested scope, makes no difference - the interpreter sees it
as an unqualified exec.

Did you actually try it in a nested scope before asserting
"nested scope or not" ?

If you just do, in the outside scope, the thing I did originally:

>>> exec('BUILD = "foobar"')
>>> BUILD
'foobar'
>>>

Then the brackets are ignored, and the defaults kick in.

But this is silly nit picking around the basic error,
which was to treat the thing as a function and putting
the brackets there.

The other bits in the thread, about the scopes and
locals() are far more interesting.

- Hendrik





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