Using __name__ inside a method references the module where the class was defined.
Is there a way instead for an object to get the module where it has been instantiated?
1 Answer
So - Python's dynamism allows a function to check the frame object where it was called from. .
It would be better if you could pass the module explicitly to the class constructor, though:
class MyObject:
def __init__(self, module):
self.module = module
...
And in the other files:
m = MyObject(__name__)
But, as I mentioned in the first line, you can get to the code calling
a module - save if you have an specialized metaclass, the code calling one class's __init__ is where the object is instantiated. So you can write:
import inspect
class MyObject:
def __init__(self, module):
caller_frame = inspect.currentframe().f_back
self.module = caller_frame.f_globals.get("__name__", "<unknown module>")
...
The Frame object is an internal Python object that keeps the execution state of a code context while the program is being run. It contain references to globals and locals variables available to that frame, as well as code object, current source line, and so on. The topmost frame (0) is the current frame in execution - the second one to the top (1) is the direct caller of the current function/method. The frame .f_globals attribute is a direct reference to the globals dictionary - the same that would be returned if one would call globals() inside that frame.
6 Comments
jsbueno
By the way, if you are writing code to try to convey functional stuff into Python, you really should get acquainted with the Frame object. Take a look at github.com/jsbueno/stackfull for more examples.
Aran-Fey
It's good practice to delete the frame object variable when you're done with it, because otherwise you risk it creating a reference cycle. It'd also be better to avoid
sys._getframe, since it's not guaranteed to exist. You can use inspect.currentframe().f_back instead.jsbueno
All objects in Python can create a "reference cycle" - if you keep references to then. Putting a
del to a variable jsut because it references a Frame is no different from deling any other variable: normally a redundant statement. (unless you are dealing with Frame objects inside a generator or async function)
Andy
Ahh, that all seems to work. Thank you. I had previously tried to use
inspect on frames but clearly was doing something wrong.jsbueno
There are projects dealign with meta programing that does this in a regular basis. Just include some serious unit testing so that one knows in advance if it works in a particular Python implementation.
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__name__inside the init of the object to store this exact information for later.__name__is passed to the constructor. But it would be nice if this wasn't necessary.