dosage/dosagelib/loader.py

# -*- coding: iso-8859-1 -*-
# Copyright (C) 2012 Bastian Kleineidam
"""
Functions to load plugin modules.
"""
import os
import importlib


def get_modules(folder='plugins'):
    """Find all valid modules in the plugins subdirectory. A valid module
    must have a .py extension, and is importable.
    @return: all loaded valid modules
    @rtype: iterator of module
    """
    dirname = os.path.join(os.path.dirname(__file__), folder)
    for modname in get_importable_modules(dirname):
        try:
            name ="..%s.%s" % (folder, modname)
            yield importlib.import_module(name, __name__)
        except ImportError as msg:
            print "ERROR: could not load module %s: %s" % (modname, msg)


def get_importable_modules(folder):
    """Find all module files in the given folder that end with '.py' and
    don't start with an underscore.
    @return module names
    @rtype: iterator of string
    """
    for fname in sorted(os.listdir(folder)):
        if fname.endswith('.py') and not fname.startswith('_'):
            yield fname[:-3]


def get_plugins(modules, classobj):
    """Find all scrapers in all modules.
    @param modules: the modules to search
    @ptype modules: iterator of modules
    @return: found scrapers
    @rytpe: iterator of class objects
    """
    for module in modules:
        for plugin in get_module_plugins(module, classobj):
            yield plugin


def get_module_plugins(module, classobj):
    """Return all subclasses of _BasicScraper in the module.
    If the module defines __all__, only those entries will be searched,
    otherwise all objects not starting with '_' will be searched.
    """
    try:
        names = module.__all__
    except AttributeError:
        names = [x for x in vars(module) if not x.startswith('_')]
    for name in sorted(names):
        try:
            obj = getattr(module, name)
        except AttributeError:
            continue
        try:
            if issubclass(obj, classobj):
                yield obj
        except TypeError:
            continue