What is the best way to do dynamic imports ?

[marcroy.olsen]

Hi list and python gurus :-)

I'm playing with some mod_python and web development. And in me code I
need to do som dynamic imports.
Right now I just do a:

exec 'import '+some_modulename

But it seems to easy, is there a "dark side" to doing it this way?
(memory use,processing ,etc)
And have to I check if the modul is already loaded?
Another thing is how to call my dynamic imported moduls.
Now I use exec (as with my modules), like this:

exec 'newclass = '+classname+'()'
newclass.somefunction()

Again it seems to easy. Is there a better/proper way to do it?
Do anybody now a good howto or tutorial to this?
Many thanks and hope you all have a happy new year :-)

/marc

[Benjamin]

On Dec 30, 8:24 am, [e-mail] wrote:

Hi list and python gurus :-)

I'm playing with some mod_python and web development. And in me code I
need to do som dynamic imports.
Right now I just do a:

exec 'import '+some_modulename

The correct way to do this is use the __import__ function. It takes
the string name of the module you want to import and returns the
module.
new_mod = __import__(some_modulename)

>
But it seems to easy, is there a "dark side" to doing it this way?
(memory use,processing ,etc)

Well, it's generally frowned on to use exec and eval.

And have to I check if the modul is already loaded?

sys.modules is a list of all imported modules, but python won't import
a module if it's already been loaded.

>
Another thing is how to call my dynamic imported moduls.
Now I use exec (as with my modules), like this:

exec 'newclass = '+classname+'()'
newclass.somefunction()

Again it seems to easy. Is there a better/proper way to do it?

If you just have the string name of a class, you have to use eval or
exec:
newclass = eval(classname)

However, if you have the class object, you can just instantiate that:
class LargeClass:
def meth(): pass
some_class = LargeClass
new_class = some_class()
some_class.meth()

>
Do anybody now a good howto or tutorial to this?

Many thanks and hope you all have a happy new year :-)

You, too!

>
/marc

[Torsten Bronger]

Hallöchen!

ma***********@gmail.com writes:

I'm playing with some mod_python and web development. And in me
code I need to do som dynamic imports. Right now I just do a:

exec 'import '+some_modulename

But it seems to easy, is there a "dark side" to doing it this way?
(memory use,processing ,etc) And have to I check if the modul is
already loaded?

I use the imp module for this:

try:
file, pathname, description = imp.find_module(full_name)
my_module = imp.load_module(full_name, file, pathname, description)
finally:
file.close()

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus
Jabber ID: br*****@jabber.org
(See http://ime.webhop.org for further contact info.)

[Gabriel Genellina]

En Sun, 30 Dec 2007 12:24:53 -0200, <ma***********@gmail.comescribi�:

I'm playing with some mod_python and web development. And in me code I
need to do som dynamic imports.
Right now I just do a:

exec 'import '+some_modulename

But it seems to easy, is there a "dark side" to doing it this way?
(memory use,processing ,etc)

Use __import__, specially if some_modulename comes from the outside.
What if some_modulename contains "modulename\nsome_nasty_function_call()"

And have to I check if the modul is already loaded?

Not needed; the standard import machinery already does that.

Another thing is how to call my dynamic imported moduls.
Now I use exec (as with my modules), like this:

exec 'newclass = '+classname+'()'
newclass.somefunction()

Again it seems to easy. Is there a better/proper way to do it?

Use getattr to obtain the desired class from the containing module, then
use it as any other class:
the_module = __import__(some_modulename)
the_class = getattr(the_module, classname)
o = the_class()
o.somefunction()

Never use exec/eval and friends - and never ever use them in a web
application!

Do anybody now a good howto or tutorial to this?

No... what do you want covered?

Many thanks and hope you all have a happy new year :-)

Thanks, and a happy new year for you too!

--
Gabriel Genellina

[marcroy.olsen]

First of thanks to all for you, especially for the quick replys.

Just need to walk the dog then I giv it a short.
On Dec 30, 3:57*pm, "Gabriel Genellina" <[e-mail]>
wrote:

>

Do anybody now a good howto or tutorial to this?

No... what do you want covered?

Nothing, think you reply coved it all.

Otherwise I will be back ;-)

[Diez B. Roggisch]

ma***********@gmail.com schrieb:

First of thanks to all for you, especially for the quick replys.

Just need to walk the dog then I giv it a short.

Please, don't kill your dog! We're a peace-loving community here that
respects dogs, and snakes and even trolls.

SCNR,

Diez