How to extract classes out of Python modules?

Question

I'm trying to write a script that takes two Bots and then feeds them to an engine for them to play a game. As an example usage:

$:python rungame.py smartbot.py dumbbot.py
Detected SmartBot in smartbot.py...
Detected DumbBot in dumbbot.py...
Running game...

The problem I'm having is that I have no idea how to detect/get the Bot objects out of the modules that are provided via the command line. (If it helps any, I wouldn't at all mind enforcing conventions.) How do I do this?

icktoofay · Accepted Answer · 2011-09-24 22:53:09Z

3

You'd probably need the class name as well a module name. With that, you could use this:

getattr(__import__(module_name), class_name)

If you don't want to make them specify a class name, you might be able to find a class that ends with Bot:

module = __import__(module_name)
clazz = None
for attribute_name in dir(module):
    attribute = getattr(module, attribute_name)
    if attribute_name.endswith('Bot') and callable(attribute):
        clazz = attribute
        break

However:

Explicit is better than implicit. —The Zen of Python

So I'd stick with the first approach of letting them specify the module and class name.

edited Sep 24, 2011 at 22:53

answered Sep 24, 2011 at 22:47

icktoofay

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1 Comment

icktoofay Over a year ago

Although probably unrelated to your application, it appears Werkzeug has some functionality which can import objects like that, too.

SingleNegationElimination · Accepted Answer · 2011-09-25 01:43:24Z

1

One of the most common patterns for this problem is to define in your API that the object must have a particular name; For instance, you might call that special variable bot:

# smartbot.py
class SmartBot(object):
    "A very smart bot!"

bot = SmartBot()

# dumbbot.py
class DumbBot(object):
    "A dumb bot bot!"

bot = DumbBot()

# rungame.py
import sys
for source in sys.argv[1:]:
    l = {}
    execfile(source, l)
    bot = l["bot"]
    print "Detected %s in %s..." % (type(bot).__name__, source)
print "Running game..."

answered Sep 25, 2011 at 1:43

SingleNegationElimination

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