Automatic instance Python

Question

Suppose you have the following structure in your src folder:

conf.py
./drivers
    mod1.py --> contains mod1Class
    mod2.py --> contains mod2Class

What I'd like to have is a snippet of code in conf.py to automatically instantiate the classes in mod*.py so that if one day I'll add mod3.py --> mod3Class this will be automatically instantiated in conf.py without adding any line of code.

I tried, without success:

from drivers import *

but I'm not able to import, I receive a NameError. So I'm stuck at the very first step. Also suppose I'm able to perform the import successfully, how can I do:

mod1Class_instance = mod1.mod1Class() (in a cycle, one instance for every file in drivers)

in an automatic way? I cannot use strings to make the instance of a class so I cannot get the names of the files in drivers and use strings. What's the right way to do this operation?

Thanks

Answer 1

Maybe, it's what you need:

from types import ModuleType

import drivers

for driver_module in dir(drivers):
    if not isinstance(driver_module, ModuleType):
        continue # not real module driver
    for cls in dir(driver_module):
        if not isinstance(cls, SomeBaseClass):
             continue # not real mod class
        # create new variable with name as lower class name
        locals()[cls.__name__.lower()] = cls()

And, also, you should create __init__.py file in your drivers folder. This will mean that your folder is a python-module.

On the other hand, I recommend manually describe all imports. This simple approach makes your code more clear.

Answer 2

This loads classes in modules in a directory drivers, which is in the same directory of the current module, and does not need to make drivers a package:

from collections import defaultdict
import os
import pkgutil


def getclasses(module):
    """Get classes from a driver module."""
    # I'd recommend another way to find classes; for example, in defuz's 
    # answer, classes in driver modules would have one base class.
    try:
        yield getattr(module, module.__name__ + "Class")
    except AttributeError:
        pass

instances = defaultdict(list)
drivers_dir = os.path.join(os.path.dirname(__file__), 'drivers')
for module_loader, name, ispkg in pkgutil.iter_modules([drivers_dir]):
    module = module_loader.find_module(name).load_module(name)
    for cls in getclasses(module):
        # You might want to use the name of the module as a key instead of the  
        # module object, or, perhaps, to append all instances to a same list.
        instances[module].append(cls())

# I'd recommend not putting instances in the module namespace, 
# and just leaving them in that dictionary.
for mod_instances in instances.values():
    for instance in mod_instances:
        locals()[type(instance).__name__ + "_instance"] = instance