你可以这样写"main.py":

#!/usr/bin/env python

__all__=["somevar", "do_something"]

somevar=""

def do_something():
    pass #blahblah

if __name__=="__main__":
    do_something()

由于Python的工作方式，当它导入模块时，有必要运行它们。

为了防止模块中的代码在导入时被执行，但只在直接运行时执行，你可以使用以下if来保护它:

if __name__ == "__main__":
    # this won't be run when imported

您可能希望将此代码放在main()方法中，以便可以直接执行文件，或者导入模块并调用main()。例如，假设这是在文件foo.py中。

def main():
    print "Hello World"

if __name__ == "__main__":
    main()

这个程序可以通过python foo.py运行，也可以通过另一个python脚本运行:

import foo

...

foo.main()

不幸的是，你不知道。这是导入语法工作的一部分，它这样做很重要——记住def实际上是执行的东西，如果Python不执行导入，你就会，嗯，没有函数。

不过，由于您可能有权访问该文件，因此您可能能够查看导致错误的原因。可以通过修改环境来防止错误的发生。

Another option is to use a binary environment variable, e.g. lets call it 'run_code'. If run_code = 0 (False) structure main.py to bypass the code (but the temporarily bypassed function will still be imported as a module). Later when you are ready to use the imported function (now a module) set the environment variable run_code = 1 (True). Use the os.environ command to set and retrieve the binary variable, but be sure to convert it to an integer when retrieving (or restructure the if statement to read a string value),

在main.py:

import os

#set environment variable to 0 (False):
os.environ['run_code'] = '0'


def binary_module():
    #retrieve environment variable, convert to integer
    run_code_val = int(os.environ['run_code'] )
    
    if run_code_val  == 0:
        print('nope. not doing it.')
    if run_code_val == 1:
        print('executing code...')
        # [do something]

.．.在任何加载main.py的脚本中:

import os,main

main.binary_module() 

输出:不。不做。

# now flip the on switch!
os.environ['run_code'] = '1'
main.binary_module()

输出:执行代码…

*注意:上面的代码假设main.py和任何导入它的脚本存在于同一个目录中。

我做了一个简单的测试:

# test.py

x = 1
print("1, has it been executed?")


def t1():
     print("hello")
     print("2, has it been executed?")


def t2():
     print("world")
     print("3, has it been executed?")


def main():
     print("Hello World")
     print("4, has it been executed?")


print("5, has it been executed?")
print(x)

# while True:
# t2()

if x == 1:
     print("6, has it been executed?")

# test2.py

import test

当执行或运行test2.py时，运行结果:

1, has it been executed?

5, has it been executed?

1

6, has it been executed?

结论:当导入的模块没有添加if __name__=="__main__":时，当前模块将运行，导入模块中不在函数中的代码将按顺序执行，而函数中未调用的代码将不执行。

此外:

def main():
    # Put all your code you need to execute directly when this script run directly.
    pass

if __name__ == '__main__':
    main() 
else:
    # Put functions you need to be executed only whenever imported

使用if __name__ == '__main__'习惯用法——__name__是一个特殊变量，如果模块作为脚本运行，其值为'__main__'，如果模块被导入，则为模块名。所以你会这样做

# imports
# class/function definitions
if __name__ == '__main__':
    # code here will only run when you invoke 'python main.py'