How to write python plug-ins for your own python program?

[Tian]

I am writing an audio game using Python. in this game you can apply
some sound effects for the clips you have recorded. I want to make this
function extensible. I want user to be able to add new sound effect
plug-ins in the future.

I want the plug-in to be a simple python code (text file) and a
description file. I will set some rules for plug-in writing (like you
must inherit some class and implement some method). I hope plugin can
be added while original program is running. Is there any good method to
read in python code and test availability and invoke the functions
inside?

Thanks


Tian

[alex23]

Re: How to write python plug-ins for your own python program?


Tian wrote:[color=blue]
> Is there any good method to
> read in python code and test availability and invoke the functions
> inside?[/color]

You mean like 'import'? :)

- alex23

[Simon Wittber]

Re: How to write python plug-ins for your own python program?

> You mean like 'import'? :)

That's how I would do it. It's the simplest thing, that works.

exec("import %s as plugin" % pluginName)
plugin.someMeth od()

where pluginName is the name of the python file, minus the ".py" extension.

Sw.

[Mark Rowe]

Re: How to write python plug-ins for your own python program?


On Mar 3, 2005, at 9:33 PM, Simon Wittber wrote:
[color=blue][color=green]
>> You mean like 'import'? :)[/color]
>
> That's how I would do it. It's the simplest thing, that works.
>
> exec("import %s as plugin" % pluginName)
> plugin.someMeth od()
>
> where pluginName is the name of the python file, minus the ".py"
> extension.[/color]

A better method would be something along the lines of:

plugin = __import__(plug inName)
plugin.someMeth od()

This avoids the potential security problem that `exec' poses as well as
the need to parse + interpret the string.

Regards,

Mark Rowe
<http://bdash.net.nz/>

[Terry Hancock]

Re: How to write python plug-ins for your own python program?

On Wednesday 02 March 2005 11:28 pm, Tian wrote:[color=blue]
> I am writing an audio game using Python. in this game you can apply
> some sound effects for the clips you have recorded. I want to make this
> function extensible. I want user to be able to add new sound effect
> plug-ins in the future.
>
> I want the plug-in to be a simple python code (text file) and a
> description file. I will set some rules for plug-in writing (like you
> must inherit some class and implement some method). I hope plugin can
> be added while original program is running. Is there any good method to
> read in python code and test availability and invoke the functions
> inside?[/color]

It's not hard to scrape the contents of a directory and import any modules
you find (i.e. to implement a "plugin directory"). I do it here (beware line-wrap):

http://cvs.sourceforge.net/viewcvs.py/narya-project/Narya1/VarImage/Operators/__init__.py?rev=1.1&view=markup

You might not want to have the reading code in the same directory as the
plugins -- you don't have to do it that way. Take a look at the __import__()
built-in in the Python Library Reference for more information.

I'm sure it's possible to run this code periodically at runtime, although I
prefer to do it only at startup (what if one of the plugins is faulty and
crashes the program?).

Cheers,
Terry

--
--
Terry Hancock ( hancock at anansispacework s.com )
Anansi Spaceworks http://www.anansispaceworks.com

[David M. Cooke]

Re: How to write python plug-ins for your own python program?

Simon Wittber <simonwittber@g mail.com> writes:
[color=blue][color=green]
>> You mean like 'import'? :)[/color]
>
> That's how I would do it. It's the simplest thing, that works.
>
> exec("import %s as plugin" % pluginName)
> plugin.someMeth od()
>
> where pluginName is the name of the python file, minus the ".py" extension.[/color]

You'd better hope someone doesn't name their plugin
'os; os.system("rm -rf /"); import sys'

Use __import__ instead.

--
|>|\/|<
/--------------------------------------------------------------------------\
|David M. Cooke
|cookedm(at)phy sics(dot)mcmast er(dot)ca

[Andrew Dalke]

Re: How to write python plug-ins for your own python program?

Mark Rowe wrote:[color=blue]
> A better method would be something along the lines of:
>
> plugin = __import__(plug inName)
> plugin.someMeth od()[/color]

In the one time I did a plugin architecture I found that


state = ... set up intial state for my program ...
...
plugin = __import__(plug inName)
plugin.someMeth od(state)


was useful because it gave the plugin a way to modify
the program state, rather than changing global variables.

Andrew
dalke@dalkescie ntific.com

[Andre]

Re: How to write python plug-ins for your own python program?

Mark Rowe <mail.python.or g@bdash.net.nz> wrote in message news:<mailman.3 293.1109840097. 22381.python-list@python.org >...[color=blue]
> On Mar 3, 2005, at 9:33 PM, Simon Wittber wrote:
>[color=green][color=darkred]
> >> You mean like 'import'? :)[/color]
> >
> > That's how I would do it. It's the simplest thing, that works.
> >
> > exec("import %s as plugin" % pluginName)
> > plugin.someMeth od()
> >
> > where pluginName is the name of the python file, minus the ".py"
> > extension.[/color]
>
> A better method would be something along the lines of:
>
> plugin = __import__(plug inName)
> plugin.someMeth od()
>
> This avoids the potential security problem that `exec' poses as well as
> the need to parse + interpret the string.
>[/color]
What happens if you have:
..def someMethod():
.. import os
.. rm * # or whatever other evil thing you might thing of

Andre

[hemanth]

Re: How to write python plug-ins for your own python program?

Andre wrote:[color=blue]
> Mark Rowe <mail.python.or g@bdash.net.nz> wrote in message[/color]
news:<mailman.3 293.1109840097. 22381.python-list@python.org >...[color=blue][color=green]
> > On Mar 3, 2005, at 9:33 PM, Simon Wittber wrote:
> >[color=darkred]
> > >> You mean like 'import'? :)
> > >
> > > That's how I would do it. It's the simplest thing, that works.
> > >
> > > exec("import %s as plugin" % pluginName)
> > > plugin.someMeth od()
> > >
> > > where pluginName is the name of the python file, minus the ".py"
> > > extension.[/color]
> >
> > A better method would be something along the lines of:
> >
> > plugin = __import__(plug inName)
> > plugin.someMeth od()
> >
> > This avoids the potential security problem that `exec' poses as[/color][/color]
well as[color=blue][color=green]
> > the need to parse + interpret the string.
> >[/color]
> What happens if you have:
> .def someMethod():
> . import os
> . rm * # or whatever other evil thing you might thing of
>
> Andre[/color]


Some time back I remember discussions on plugin risks in
Leo (leo.sf.net). The conclusion was someone can always harm
your system by writing a nasty plugin. Hence you should always
use plugins from sources you can trust. I don't know if there
is any alternative way in Python to have safe third party
plugins.

[Reinhold Birkenfeld]

Re: How to write python plug-ins for your own python program?

David M. Cooke wrote:[color=blue]
> Simon Wittber <simonwittber@g mail.com> writes:
>[color=green][color=darkred]
>>> You mean like 'import'? :)[/color]
>>
>> That's how I would do it. It's the simplest thing, that works.
>>
>> exec("import %s as plugin" % pluginName)
>> plugin.someMeth od()
>>
>> where pluginName is the name of the python file, minus the ".py" extension.[/color]
>
> You'd better hope someone doesn't name their plugin
> 'os; os.system("rm -rf /"); import sys'[/color]
^
Well, that would be difficult, but "rm -rf ~" would work rather nicely...

Of course, one could test pluginName that it contains only
alphanumerics, but
[color=blue]
> Use __import__ instead.[/color]

is surely the better solution.

Reinhold