父类init在继承期间执行

Question

One basic question in OOP.

test.py file content:

class test(object):
    def __init__(self):
        print 'INIT of test class'
obj=test()

Then I opened another file.

I just inherited from the above test class:

from test import  test
class test1(test):
    def __init__(self):
        pass

So when I run this class, the init from parent class is executing.

I read that I can avoid it by using

if __name__='__main__'

I can over come this, but my question is why the parent class's init is executing as I am just importing this class only in my second file, how the object creation code executed?

Answer 1

Importing a module executes all module-level statements, including obj=test() . To avoid this, make an instance only when run as the main program, not when imported:

class test(object):
    def __init__(self):
        print 'INIT of test class'

if __name__ == '__main__':
     obj=test()

The problem is not the inheritance but the import. In your case you execute obj=test() when importing:

from test import test

When you import test , its name __name__ is test . But when you run your program on the command line as main program with python test.py , its name is __main__ . So, in the import case, you skip obj=test() if you use:

if __name__ == '__main__':
     obj=test()