How can I use context vars in other file in python 3.7 or above?

Question

I have a context var in in file a.py and I want to use it in b.py.

a.py:

import contextvars

cntx = contextvars.ContextVar("abcd")

b.py:

from .a import cntx

print(cntx.get())

Error:

Traceback (most recent call last):
  File "/home/user/Desktop/b.py", line 1, in <module>
    from .a import cntx
ImportError: attempted relative import with no known parent package

Isn't this how context variables supposed to work? I'm using python 3.9

from ./a import cntx is throwing syntax error at / and from a import cntx is throwing LookupError: it — Aravindh, Nov 16 '22 at 10:43
Does this answer your question? [Relative imports in Python 3](https://stackoverflow.com/questions/16981921/relative-imports-in-python-3) — Jamiu S., Nov 16 '22 at 10:46
@Jay because that is not valid python syntax. It doesn't even compile. — juanpa.arrivillaga, Nov 16 '22 at 11:11

Jay · Accepted Answer · 2022-11-16T11:00:14.430

The ImportError that you are getting is because of the invalid file name. .a is a valid file name and would work if you had a file with filename being .a.py

The reason you are getting the LookupError: <ContextVar name='abcd' at 0x7f7d6209c5e0> is because you are trying to get() the context which hasn't been set yet.

The get() method raises a LookupError if no context was set before.

Try with following -

a.py:

import contextvars

cntx = contextvars.ContextVar("abcd")
cntx.set("example")

b.py:

from a import cntx
print(cntx.get())

When you run b.py -

Output:

example

How can I use context vars in other file in python 3.7 or above?

1 Answers1