global varname

[snippsat]

Can do it like this.

# sitecustomize.py
import builtins

builtins.varname = 100

Save sitecustomize.py in Path of Python that you use,eg root folder.
Now in any function without import will varname work as a builtin-in.

def somefunc(number: int) -> list[int]:
    lst = []
    lst.append(number * varname)
    lst.append(number * 4)
    return lst

print(somefunc(5))

Output:
[500, 20]