从导入模块中的父模块调用函数

Question

I have following problem: I have a .py file with some defined functions and I import a module. From this imported module I want do call a function from the parent module. How do I do this? I searched a lot but didn't found an answer. Here is some test code to show you my problem.

File 1:

from test2 import *

def one():
    print("one")
    pass

def two():
    print("two")
    print("now call function three from test one")

    three()


one()
two()

File 2: Imported as module

def three():
    print("three")
    print("now call function one from test 1")

    one()

Answer 1

You may pass function as parameter:

Test 1:

from test2 import *

def one():
    print("one")
    pass

def two():
    print("two")
    print("now call function three from test one")

    three(one)  # function one()


one()
two()

Test 2:

def three(function):
    print("three")
    print("now call function one from test 1")

    function()

Answer 2

More pythonic solution (IMHO) is this:

File test1.py :

import test2

def one():
    print("one")
    pass

def two():
    print("two")
    print("now call function three from test one")

    test2.three()

if __name__ == '__main__':
    one()
    two()

and test2.py :

import test1

def three():
    print("three")
    print("now call function one from test 1")

    test1.one()

then python3 test1.py produces:

one
two
now call function three from test one
three
now call function one from test 1
one

Yes, there is a circular import. Let's go step by step to see how it works:

1. test1 is started as __main__ , because that's the special reserved name Python uses for starting programs.
2. test1 imports test2 in its first line, so the parsing continues there.
3. test2 in turn imports test1 , that's why the first file is parsed again from the beginning, but now under its real name. The import test2 is this time skipped, because test2 is already a known module. At the end of the file, the __name__ is not __main__ and the if condition is false. This is important! Importing should not have any side effects.
4. control is returned to test2 , the rest of file is parsed.
5. control is returned to test1 , the rest of file is parsed. The condition at the bottom of the file is satisfied this time, so the execution of the main part starts with one()