Dynamic module import of class list from module given its full path

Question

First, it seems proper to me to state that I've read over the following questions:

And, I don't feel like they address my use case. That said, here's my question:

How can I dynamically import from a configuration file like this:

[imports]
/var/imports/foo.py = baz monkey
/var/imports/bar.py = ape

So that I can call the known objects via RESTful interface like this.

# http://localhost/data?operation=get&class=baz&id=1
def handler(object):
  def handle(self):
    cls = instantiate(request.args["class"])
    meth = request.args["operation"]
    return getattr(cls,meth,request.args)

And it could respond with the result of get() on an instance of that class.

I'm not sure that I've understood the question. Where the import configuration fits in this code? How and why do you use it? — frm, Feb 28 '11 at 17:51
This is exactly the kind of thing addressed by webapp frameworks like Django. Additionally, you seem to make no distinction between classes and instances. — Apalala, Feb 28 '11 at 18:04

score 2 · Answer 1 · answered Feb 28 '11 at 18:01

Look at the 2nd link again. It already mentions imp.load_source:

import imp

# some sort of shared dict for everything imported
loaded = {}

def load(path, from_list):
    # load the path
    module = imp.load_source( "dummy", path)
    for name in from_list:
        # add the names
        loaded[name] = getattr(module, name)

#lets say you have this:
data = "/var/imports/foo.py", ["baz"]
load(*data)
print loaded['baz'] # whatever foo.baz was

Now you can do something like this:

def instantiate( clsname ):
    obj = loaded[clsname]
    return obj()

I hope this gets you started.

score 1 · Accepted Answer · answered Feb 28 '11 at 17:58

Here's a rough sketch of a class registry you could use like this:

class ClassRegistry(object):

    def __init__(self):
        self.classes = {}

    def add_file_classes(self, fname, class_list):
        globals = {}
        exec open(fname) in globals
        for class_name in class_list:
            self.classes[class_name] = getattr(globals, class_name)

    def get_class(self, class_name):
        return self.classes[class_name]

Read your config file and invoke add_file_classes like this:

reg = ClassRegistry()
reg.add_file_classes("/var/imports/foo.py", ["baz", "monkey"])
reg.add_file_classes("/var/imports/bar.py", ["ape"])

then later:

cls = reg.get_class("baz")

Note that we aren't actually importing the files, simply executing them and collecting their results.

Dynamic module import of class list from module given its full path

2 Answers2