ContextVars demonstration

contextvars.py

# Demonstration of using ContextVars instead of global variables.

# Set to True for global mode, False for ContextVar mode
global_mode = False

# With a global variable, the result is: 1 2 3 3 3 3 3 3 3
# With a ContextVar, the result is:      1 2 3 1 2 3 1 2 3

import asyncio
import contextvars


N = None

Nvar = contextvars.ContextVar("my_number_var")


async def print_N():
    if global_mode:
        global N
        print(N, end=" ")
    else:
        print(Nvar.get(), end=" ")


async def printloop(n):
    if global_mode:
        global N
        N = n
    else:
        Nvar.set(str(n))

    for i in range(3):
        await print_N()
        await asyncio.sleep(0.1)


async def main():
    await asyncio.gather(
        printloop(1),
        printloop(2),
        printloop(3)
    )

asyncio.run(main())