导入了Python模块; 为什么重新分配其中的成员也会影响其他地方的进口？

Question

I am seeing Python behavior that I don't understand. Consider this layout:

project
|   main.py
|   test1.py
|   test2.py
|   config.py

main.py:

import config as conf
import test1
import test2

print(conf.test_var)
test1.test1()
print(conf.test_var)
test2.test2()

test1.py:

import config as conf

def test1():
    conf.test_var = 'test1'

test2.py:

import config as conf

def test2():
    print(conf.test_var)

config.py:

test_var = 'initial_value'

so, python main.py produce:

initial_value
test1
test1

I am confused by the last line. I thought that it would print initial_value again because I'm importing config.py in test2.py again, and I thought that changes that I've made in the previous step would be overwritten. Am I misunderstanding something?

Answer 1

Python caches imported modules. The second import call doesn't reload the file.

Answer 2

test2.py

import config as conf

def test2():
    print(id(conf.test_var))
    print(conf.test_var)

test1.py

import config as conf

def test1():
    conf.test_var = 'test1'
    print(id(conf.test_var))

Change code like this.

And run main.py

initial_value
140007892404912
test1
140007892404912
test1

So, you can see that in both cases you are changing value of the same variable. See these id 's are same.

Answer 3

You edited the test_var in test1.py and then just printed it again using test2.py . Importing again does not change the fact than you assigned new value to the variable - it does not "reset" the value to the first one.

Answer 4

You changed the value of test_var when you ran test1 , and so it was already changed when you ran test2 .

That variable will not reset for every file in which you import it. It will be one value for everything.

Answer 5

no, you're changing with test1() in the config.py a constant value. This won't be resetted. Since you print it in test2() , the modified value gets printed again.