Trying to understand dependency injection - python-3.x

Question

I am trying to learn the concept of "dependency injection" in Python. First, if anyone has a good reference, please point me at it.
As a project I took the use case of changing logic and formatting based on options passed to the linux command "mtr"
The dependency client class is MtrRun. The initial dependency injection service is DefaultRgx (I plan to add a couple more). The injection interface is MtrOptions. And the injector class is just called Injector.
class MtrRun(MtrOptions): # Dependency injection client
def __init__(self, MtrOptions, options, out):
self.MtrOptions = MtrOptions
self.options = options
self.out = out
def mtr_options(self, options, out):
return self.MtrOptions.mtr_options(options, out)
class DefaultRgx(MtrOptions): # Dependency injection service
def __init__(self, options):
self.options = None
def mtr_options(self, options, out):
pass # code abbreviated for clarity
class MtrOptions(): # Dependency injection interface
def __init__(self, svc):
self.svc = svc
def mtr_options(self, options, out):
return self.svc.mtr_options(options, out)
class Injector(): # Dependency injection injector
def inject(self):
MtrOptions = MtrOptions(DefaultRgx())
mtr_result = MtrRun(MtrOptions)
This snippet will not clear a lint. My IDE claims that the MtrOptions class passed into the injection client and service are not defined. When I try to resolve it, a new MtrOptions class is created, but the error persists. I am certain I just don't know what I am doing. Conceptually I admit a weak grasp. Help is appreciated.

Answer 1

So I messed up several ways. I did not understand the declarative way to establish inheritance. Nothing in my example actually was an "object". Second, order appears to matter. The object classes seem to need to appear before their children. Third, the injector class needs to include both sides of the classes to be injected.
class DefaultRgx(object): # Dependency injection service
def __init__(self, options):
self.options = None
def mtr_options(self, options, out):
mtr_result = ['Do stuff the old way']
return mtr_result
class MtrRun(DefaultRgx): # Dependency injection client
def __init__(self, host, count, options):
self.count = count
self.host = host
self.options = options
def mtr_module(self, host, count, options):
mtr_result = super().mtr_options(options, out)
return mtr_result
class MtrOptions(DefaultRgx): # Dependency injection interface
def mtr_options(self, options, out):
mtr_result = ['I was injected instead of DefaultRgx']
return mtr_result
class Injector(MtrOptions, MtrRun): # Dependency injection injector
pass
def main():
mtr = Injector(os.getenv('HOST'), os.getenv('COUNT'), None)
mtr_result = mtr.mtr_module()
This linted correctly. I have not run it yet, but conceptually that YouTube really helped things click. Thank you so much.