如何从main引用嵌套在类中的定义变量

Question

I would like to know how (in Python) to reference a variable that is inside a def, inside a class. For example:

class class_name():
    .
    .    # Some more definitions in here
    . 

    def definition_name():
        variable_of_interest = 10    # 10 chosen arbitrarily
    .
    .    # Some more definitions in here
    .

if __name__ == '__main__': 
    # Here I want to reference variable_of_interest. Example:
    if variable_of_interest = 10
        do stuff

Even better, how can I reference the variable in main if the example looks like:

class class_name():

    def __init__(self):
        # Some code
        def _another_definition():
            variable_of_interest = 10

if __name__ == '__main__':
    #same as before

So basically how do I reference a variable that is placed like Class()>Def()>Def()>Variable in main?

Answer 1

What you're calling a def is actually either a function or in this case a method in a class.

Variables defined in a method are normally not available. That's the whole idea of encapsulation .

If you want to access variables in a class they should either class or instance variables.

A variable defined in an instance, a member , would need to be accessed as part of an instance of the class. It's defined in __init__() .

For example:

class MyClass:
    def __init__(self):
        self.data = []

Accessed as:

x = MyClass() # instantiate an object of this class
x.data # access instance member

A class variable can be defined at the top of the class definition:

class MyClass:
    """A simple example class"""
    i = 12345

Then it would be accessed with MyClass.i .

Look at this Python tutorial on classes to understand this better.

If you really want to have a variable in a class method also be accessible directly in the main context then you can make it a global variable by preceding it with global . Otherwise variables are by default local and only accessible in the same scope.