Question about name scope
Dave Angel
d at davea.name
Wed Feb 1 18:36:36 CET 2012
On 02/01/2012 12:11 PM, Olive wrote:
> I am learning python and maybe this is obvious but I have not been able
> to see a solution. What I would like to do is to be able to execute a
> function within the namespace I would have obtained with from<module>
> import *
>
> For example if I write:
>
> def f(a):
> return sin(a)+cos(a)
>
> I could then do:
>
> from math import *
>
> f(5)
>
> But I have polluted my global namespace with all what's defined in
> math. I would like to be able to do something like "from math import *"
> at the f level alone.
>
> The main reason for this is the sympy module for CAS (computer algebra).
> It reimplement a lot of functions and define all the letters as symbolic
> variables. Writing sympy.<function> everywhere is inconvenient.
> Importing all the symbols in the global namespace would lead to name
> clash. It would be nice if I could import all the sympy names but for a
> given function only.
>
> Olive
>
>
Start by specifying python version and operating system.
I tried your experiment using Python 2.7 and Linux 11.04
def f(a):
from math import sin, cos
return sin(a) + cos(a)
print f(45)
Does what you needed, and neatly. The only name added to the global
namspace is f, of type function.
I was a bit surprised that using from math import * inside the
function worked, but it generates a warning:
olive.py:2: SyntaxWarning: import * only allowed at module level
def f(a):
I normally avoid any use of the "from XX import *" form, as it pollutes
the global name space. The only exception is when a library writer
documents that this is the "normal" way to interface to it. In this
case, he usually defines just a few things that are visible this way)
What I do is put a single import math at the top of my source file, and
use math.sin, and math.cos where needed. Occasionally, I'll use
something like:
from math import sin,cos
at the top, so I know just which symbols I'm defining.
How about:
import math
def f(a):
sin = math.sin
cos = math.cos
return sin(a) + cos(a)
print f(45)
This lets you explicitly use the sin and cos names inside the function,
by defining them at entry to the function.
--
DaveA
More information about the Python-list
mailing list