Why is Python running my module when I import it, and how do I stop it?

Unfortunately, you don’t. That is part of how the import syntax works and it is important that it does so — remember def is actually something executed, if Python did not execute the import, you’d be, well, stuck without functions.

Since you probably have access to the file, though, you might be able to look and see what causes the error. It might be possible to modify your environment to prevent the error from happening.

Use the if __name__ == '__main__' idiom — __name__ is a special variable whose value is '__main__' if the module is being run as a script, and the module name if it’s imported. So you’d do something like

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

You may write your “main.py” like this:

#!/usr/bin/env python

__all__=["somevar", "do_something"]

somevar=""

def do_something():
    pass #blahblah

if __name__=="__main__":
    do_something()

Due to the way Python works, it is necessary for it to run your modules when it imports them.

To prevent code in the module from being executed when imported, but only when run directly, you can guard it with this if:

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

You may want to put this code in a main() method, so that you can either execute the file directly, or import the module and call the main(). For example, assume this is in the file foo.py.

def main():
    print "Hello World"

if __name__ == "__main__":
    main()

This program can be run either by going python foo.py, or from another Python script:

import foo

...

foo.main()

Try just importing the functions needed from main.py? So,

from main import SomeFunction

It could be that you’ve named a function in batch.py the same as one in main.py, and when you import main.py the program runs the main.py function instead of the batch.py function; doing the above should fix that. I hope.

Put the code inside a function and it won’t run until you call the function. You should have a main function in your main.py. with the statement:

if __name__ == '__main__':
  main()

Then, if you call python main.py the main() function will run. If you import main.py, it will not. Also, you should probably rename main.py to something else for clarity’s sake.

Although you cannot use import without running the code; there is quite a swift way in which you can input your variables; by using numpy.savez, which stores variables as numpy arrays in a .npz file. Afterwards you can load the variables using numpy.load.

See a full description in the scipy documentation

Please note this is only the case for variables and arrays of variable, and not for methods, etc.

There was a Python enhancement proposal PEP 299 which aimed to replace if __name__ == '__main__': idiom with def __main__:, but it was rejected. It’s still a good read to know what to keep in mind when using if __name__ = '__main__':.

I did a simple test:

#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

When executing or running test2.py, the running result:

1, has it been executed?

5, has it been executed?

1

6, has it been executed?

Conclusion: When the imported module does not add if __name__=="__main__":, the current module is run, The code in the imported module that is not in the function is executed sequentially, and the code in the function is not executed when it is not called.

in addition：

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

A minor error that could happen (at least it happened to me), especially when distributing python scripts/functions that carry out a complete analysis, was to call the function directly at the end of the function .py file.
The only things a user needed to modify were the input files and parameters.
Doing so when you import you’ll get the function running immediately. For proper behavior, you simply need to remove the inside call to the function and reserve it for the real calling file/function/portion of code

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). If later if you are ready to use the function 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),

in 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]

…

…

in whatever script is loading main.py:

import os,main

initial2.binary_module() 

OUTPUT: nope. not doing it.

# now flipt the on switch!
os.environ['run_code'] = '1'
initial2.binary_module()

OUTPUT: executing code…

*Note: The above code presumes main.py and whatever script imports it exist in the same directory.