Python: Create a member that is a instance of its class

Question

I am very confused that I did not directly found a topic about my concern:

I got the class RoadMark. In this class, I wanna create a member that is a specific instance of that class. But I am not able to call the constructor.

I tried:

calling the init function (but it has no return, so its worthless)
define the member as a function with the @property attribute (but these returns cannot have members, so worthless for an object)
Trying "solid = self.RoadMark..." (also not working)
Using a factory function to create the object (but in the method, RoadMark is also not defined)

Is there a way to solve my problem or do I have to outsource the "solid" variable?

Kind regards

Please show errors and code as text in the question. No screenshots — Mad Physicist, Oct 16 '19 at 12:34
possible duplicate of https://stackoverflow.com/questions/14841203/python-instantiate-class-within-class-definition — gogaz, Oct 16 '19 at 12:36
if you are looking for singleton instance creation, pfb link; https://stackoverflow.com/questions/6760685/creating-a-singleton-in-python — nanda kumar gowda, Oct 16 '19 at 12:39

score 5 · Answer 1 · answered Oct 16 '19 at 12:36

5

You can assign it to the class member after the class definition.

class RoadMark:
    ...
RoadMark.solid = RoadMark()

answered Oct 16 '19 at 12:36

Chao Peng

149
7

score 1 · Accepted Answer · answered Oct 16 '19 at 12:42

Python code is executed as it is encountered. When the interpreter encounters the line class RoaMark:, it starts creating a new class object. Then it starts to run the code inside the class body to determine the attributes of the class. When the code in the body is running, the class object does not exist yet, so you can't access it. What you can do is wait until the class is created before assigning an attribute to it:

class RoaMark:
   ...

RoaMark.solid = RoaMark(...)

Python: Create a member that is a instance of its class

2 Answers2