Problem with exec

[Justus Schwabedal]

I'm trying to parallise with python. Specifically I'm sending code to
the processes and let them exec this code (in ascii form). However I
ran into a problem with Namespaces (I think) which I do not understand.

Here's what I do first:
---------------------------------------
bash-3.2$ cat execBug.py
#! /usr/bin/python
header="""
from scipy import randn
def f():
return randn()
"""
exec header
print "f() =",f()

bash-3.2$ ./execBug.py
f() = 0.633306324515


it est: it works.
However when I do this:

bash-3.2$ cat execBug2.py
#! /usr/bin/python
header="""
from scipy import randn
def f():
return randn()
"""
def g():
exec header
return f()
print "g() =",g()
bash-3.2$ ./execBug2.py
g() =
Traceback (most recent call last):
File "./execBug2.py", line 10, in <module>
print "g() =",g()
File "./execBug2.py", line 9, in g
return f()
File "<string>", line 4, in f
NameError: global name 'randn' is not defined
bash-3.2$ ???

I get this global name error. I can fix it with adding some line like
"global randn" but I don't want to do this. I want to do exactly what
I wrote: Import the function scipy.randn in the local namespace of the
function "g" so that "return f()" makes sense. Can anybody help me out?
Yours Justus

[alitosis@gmail.com]

Re: Problem with exec

On Mar 14, 9:47 am, Justus Schwabedal <justus.schwabe ...@gmx.de>
wrote:
[snipped]

However when I do this:
>
bash-3.2$ cat execBug2.py
#! /usr/bin/python
header="""
from scipy import randn
def f():
return randn()
"""
def g():
exec header
return f()
print "g() =",g()
bash-3.2$ ./execBug2.py
g() =
Traceback (most recent call last):
File "./execBug2.py", line 10, in <module>
print "g() =",g()
File "./execBug2.py", line 9, in g
return f()
File "<string>", line 4, in f
NameError: global name 'randn' is not defined
bash-3.2$ ???
>
I get this global name error. I can fix it with adding some line like
"global randn" but I don't want to do this. I want to do exactly what I wrote: Import the function scipy.randn in the local namespace of the
>
function "g" so that "return f()" makes sense. Can anybody help me out?
Yours Justus

Maybe using an explicit namespace is good enough for your needs:

#! /usr/bin/python
header="""
from scipy import randn
def f():
return randn()
"""
def g():
n = {}
exec header in n
return n['f']()
print "g() =",g()


(i don't understand the issues, but I can cut-and-paste with the best
of them)

[Justus Schwabedal]

Re: Problem with exec


On Mar 14, 2008, at 4:41 AM, alitosis@gmail. com wrote:

On Mar 14, 9:47 am, Justus Schwabedal <justus.schwabe ...@gmx.de>
wrote:
[snipped]

>However when I do this:
>>
>bash-3.2$ cat execBug2.py
>#! /usr/bin/python
>header="""
>from scipy import randn
>def f():
> return randn()
>"""
>def g():
> exec header
> return f()
>print "g() =",g()
>bash-3.2$ ./execBug2.py
>g() =
>Traceback (most recent call last):
> File "./execBug2.py", line 10, in <module>
> print "g() =",g()
> File "./execBug2.py", line 9, in g
> return f()
> File "<string>", line 4, in f
>NameError: global name 'randn' is not defined
>bash-3.2$ ???
>>
>I get this global name error. I can fix it with adding some line like
>"global randn" but I don't want to do this. I want to do exactly
>what I wrote: Import the function scipy.randn in the local
>namespace of the
>>
>function "g" so that "return f()" makes sense. Can anybody help me
>out?
>Yours Justus

>
Maybe using an explicit namespace is good enough for your needs:
>
#! /usr/bin/python
header="""
from scipy import randn
def f():
return randn()
"""
def g():
n = {}
exec header in n
return n['f']()
print "g() =",g()
>
>
(i don't understand the issues, but I can cut-and-paste with the best
of them)
--
http://mail.python.org/mailman/listinfo/python-list

That's what I was looking for: It's probably even a faster solution
than declaring all the imports global, isn't it?