CODEWITHSUNDEEP
python
vectro404
vectro404

Reputation: 49

Python module being reimported when imported at different places

I am relatively new to python and I have a simple python module with some constants which are being modified by some code in other files. I want these to be the same through out. i.e

a.py

start = True

b.py

import a
while(a.start):
 //do something

c.py

import a
a.start =False

My understanding of a python module is, it acts like a singleton and any module is imported only once. So, when I try running b.py and then run c.py, what I am expecting would be this:

But, when I run this I think what is happening is module is being re-imported as a duplicate and by b.py never stops running. Is there something I am doing something very basic wrong?

Upvotes: 2

Views: 108

Answers (2)

user4815162342
user4815162342

Reputation: 155046

As Martijn explained, Python modules are singletons within the same process. To achieve what you are trying to do, you need to implement some form of interprocess communication. To take a trivial example, you could write to a file:

# a.py
import os

REQUEST_FILE = 'stop-request'

def should_stop():
    return os.path.exists(REQUEST_FILE)

def clear():
    if os.path.exists(REQUEST_FILE):
        os.unlink(REQUEST_FILE)

def request_stop():
    with open(REQUEST_FILE, 'w'):
        pass

# b.py
import a
a.clear()     # avoid leftover stop-request stopping us before we've started
while not a.should_stop():
    # ... do something ...

# c.py
import a
a.request_stop()

Upvotes: 2

Martijn Pieters
Martijn Pieters

Reputation: 1122342

Python modules are singletons within one run of the interpreter.

Running c.py in a separate process will not alter the value of start in another Python interpreter.

Upvotes: 5

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