使用 locate 动态实例化类

Question

I am trying to instantiate a class dynamically from a string that is fed to a method.

from pydoc import locate
name = "folder.subfolder.classname"
my_class = locate(name)
instance = my_class()

Doing this results in an error:

TypeError: 'module' object is not callable

My question is: how can I dinamically know which class I need to call? If I hardcode the value and do my_class.classname() I can instantiate it, but I want that last part to be dynamic, instead of hardcoded. How can I do that?

Answer 1

Edit 2:

This solution will gather all classes available in the module the user provides, and then simply instantiates the first class.

import inspect
from pydoc import locate
name = "folder.subfolder.classname"
my_module = locate(name)

all_classes = inspect.getmembers(my_module, inspect.isclass)
if len(all_classes) > 0:
    instance = all_classes[0][1]()

Edit:

Gathered from the comments I believe the following code will work for your use case:

from pydoc import locate
name = "folder.subfolder.classname"
my_module = locate(name)
class_name = name.rsplit('.')[-1]
my_class = getattr(my_module, class_name)
instance = my_class()

You do seem to be a bit confused as to what modules are which resulted in our miscommunication. class.py doesn't point to a class, but to a module. In that module (your class.py file) there can be multiple classes. For the answer above I just assume that in your class.py file you have a class with the same name as the file.

Original Answer:

Well as your error shows, your my_class variable is actually a module object. The name you provide doesn't actually point to your class but to the module containing the class.

To get a class from a module object by string you can do:

my_class = getattr(module, class_name)

and then like in your example code you can instantiate it like this:

instance = my_class()

To bring it all together:

module_name = "folder.subfolder.module_name"
my_module = locate(module_name)
my_class = getattr(my_module, class_name)
instance = my_class()

Answer 2

You didn't locate the class inside of the file:

from pydoc import locate
name = "folder.subfolder.filename.classname"
my_class = locate(name)
instance = my_class()