在不同的文件中导入相同的模块

Question

Supposing I have written a set of classes to be used in a python file and use them in a script (or python code in a different file). Now both the files require a set of modules to be imported. Should the import be included only once, or in both the files ?

File 1 : my_module.py .

import os

class myclass(object):
    def __init__(self,PATH):
        self.list_of_directories = os.listdir(PATH)

File 2 :

import os
import my_module

my_module.m = myclass("C:\\User\\John\\Desktop")

list_ = m.list_of_directories

print os.getcwd()

Should I be adding the line import os to both the files ?

How does this impact the performance, supposing there are lots of modules to be imported ? Also, is a module ,once imported, reloaded in this case ?

Answer 1

Each file that you are using a module in, must import that module. Each module is its own namespace. Things you explicitly import within that file are available in that namespace. Thus, if you need os in both files, you should import them in both files.