Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
338 views
in Technique[技术] by (71.8m points)

python - Introspect calling object

How do I introspect A's instance from within b.func() (i.e. A's instance's self):

class A():
    def go(self):
        b=B()
        b.func()

class B():
    def func(self):
        # Introspect to find the calling A instance here
See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

In general we don't want that func to have access back to the calling instance of A because this breaks encapsulation. Inside of b.func you should have access to any args and kwargs passed, the state/attributes of the instance b (via self here), and any globals hanging around.

If you want to know about a calling object, the valid ways are:

  1. Pass the calling object in as an argument to the function
  2. Explicitly add a handle to the caller onto b instance sometime before using func, and then access that handle through self.

However, with that disclaimer out of the way, it's still worth knowing that python's introspection capabilities are powerful enough to access the caller module in some cases. In the CPython implementation, here is how you could access the calling A instance without changing your interfaces:

class A():
    def go(self):
        b=B()
        b.func()

class B():
    def func(self):
        import inspect
        print inspect.currentframe().f_back.f_locals['self']

if __name__ == '__main__':
    a = A()
    a.go()

Output:

<__main__.A instance at 0x15bd9e0>

This might be a useful trick to know about for debugging code sometimes. But it would not be a sensible design decision to ever access the stack frames like this in the case that B.func actually needed to use A for any reason.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...