我所有的Python模块都应该显式导入相同的基本模块吗？

Question

For example: main.py:

import pygame
import mycolors
color1 = mycolors.blue

mycolors.py:

import pygame
blue = pygame.Color(0, 0, 255)

My question specifically concerns the "import pygame" present in both files. Is it really necessary to import it within each module that requires it? (answer seem to be yes, it won't run without it.) Also, does this actually get imported twice? does this have performance ramifications?

Answer 1

The module is only imported once, so you don't have to worry about wasted resources. You can see all the modules that have been imported anywhere in sys.modules . When the module is imported the second/third/etc. time you just get a reference to the module already in sys.modules

The reason you have to import it into both of the other modules is that it gets added to their namespace

This is very important in larger programs when there may be lots of modules with the same name, so you definitely wouldn't want a module to pop up in every other namespace whenever you imported it

Answer 2

I don't think these are the entire source files you're showing here. As they are now, import pygame is not necessary in main.py since you're not referencing it anywhere in that module.

As for performance: It's not going to hurt perceptibly to import the same module several times. The "real" import (with the possible compilation step) happens only once.