导入包含类的文件时，是否初始化 class 属性？

Question

I'm a beginner in python, so please bear with me. I read somewhere that when you import a file, it's exactly as if you executed that file. This confused me because I started wondering whether class attributes also get initialized when importing.

Let me give you an example,
Say we have this file named cat.py:

#cat.py
class RawFeature:
    bat = 5

And we have another file here:

import cat as c

#Does 'bat' get initialized upon calling?  
print(c.RawFeature.bat)

Does 'bat' get initialized upon calling or when the 'cat.py' file is imported?

If it gets initialized upon importing this really changes the flow of the script because let's say the class variable 'bat' is initialized by calling some function...

Answer 1

RawFeature.bat will be initialized as soon as you import the module cat or anything from the module like RawFeature . As a quick litmus test, if you store the following in a file called thing.py ,

def initialize():
    print('Calling initialize')
    return 5


class Thing:
    class_attr = initialize()

then try to import thing or Thing in a Python REPL shell, you'll noticed that Calling initialize gets printed before making any further calls.

Answer 2

@rajith-thennakoon -

Adding to kingkupps reponse, If you want your class/methods/anyCodeSnippet to restrict from getting initialized while being imported, you can add the class/methods/anyCodeSnippet in the if block as mentioned below.

if __name__ == "__main__":
    def initialize():
        print('Calling initialize')
        return 5
    class Thing:
        class_attr = initialize()