[Tutor] Confused "from module import Name" better than "import module"?

Kent Johnson kent37 at tds.net
Mon Jul 11 18:30:16 CEST 2005

Mike Hansen wrote:
> I'm confused. I was just reading the URL below..
> http://jaynes.colorado.edu/PythonGuidelines.html
> and this statement confused me: "Always use from module import Name, Name2, 
> Name3.. syntax instead of import module or from module import *. This is more 
> efficient, reduces typing in the rest of the code, and it makes it much easier 
> to see name collisions and to replace implementations."
> To me, import module is more explicit.
> It seems to easier to read CoolModule.niceFunction() than just niceFunction(). 
> You know exactly where niceFunction comes from especially when you've imported 
> many modules. Don't you avoid namespace pollution too by using import module 
> instead of from module import * or from module import Name, Name2, Name3...?

from module import * is problematic and discouraged. It causes namespace pollution and makes it harder to find out where a name is defined.

Other than that I think it is personal preference.

I often use from module import name because it reduces typing at the point of use. It is still easy to find out where a name comes from by searching for the name in the module. This adds a few names to the global namespace but it is just the ones you use, nothing like what you can get with from module import *.

I'm not sure what efficiency he is talking about - it might be faster to look up a global name than to look up a name in a module but I would want to test that. Anyway it is clearly a premature optimization and if you have code where the cost of name lookup is hurting you then you will want to convert the name to a local name, not a global.

I guess it could be easier to replace the implementation, for example if you split a module you could change
from module import Name1, Name1
from module1 import Name1
from module2 import Name2
and the rest of the client code wouldn't have to change.

my two cents

More information about the Tutor mailing list