create subclass' instance from base class and target class name

get_subclasses.py

def all_subclasses(model):
    """Gets the model from a given key."""
    return set(model.__subclasses__()).union([s for c in model.__subclasses__() for s in all_subclasses(c)])

def get_model_from_key(model, key):
    models = {klass.__name__: klass for klass in all_subclasses(model)}
    return models.get(key, None)

class BaseModel(object):
    pass
    
class Testdesu(BaseModel):
    pass
    
val = {'class_name': 'Testdesu'}

try:
    klass = get_model_from_key(BaseModel, val['class_name'])
    obj = klass()
except (KeyError, TypeError):
    pass