what is the scope of an imported function in python 3

Question

Say we have a python script with:

def add(a):
   a += b
   print(a)
b=5
add(3)

this outputs:8

but if we import the function add from another python file some_utils.py

from some_utils.py import add

b=5
add(3)

this comes back with an error that b is not defined

How to get around this ?

PS the main idea is not to pass a lot of variables every time to that function

Answer 1

The free variable b inside add refers to the global b in the module where add is defined , not the one in which it eventually is called. The following would work:

from some_utils import add
import some_utils

some_utuils.b = 5  # Set the variable add() looks for
add(3)

A better solution might be to employ a closure:

def make_add(b):
    def add(a):
        a += b
        print(a)
    return add

then

from some_utils import make_add

add = make_add(5)
add(3)

Answer 2

You're not importing the variable b, only the add function. Within the isolated scope of this function, b indeed does not exist. It exists only in the scope of the outer module, and you have two isolated b variables here. The only way to get the second one to be passed to the add function is through a parameter

The scope of an imported variable (or function/module/class) is the same scope of where the import is started (imports don't need to be at the top of the file), but this is unrelated to your error

Answer 3

Why don't you use default arguments!

def add(a, b=5):
   a += b
   print(a)

#If b is not passed, default value of 5 is used
add(3)
#If b is passed, the value of 6 is used
add(3, 6)

The output will be

8
9

b is not defined outside your script, that is why you cannot access in outside your script, if you want to access it outside, you can also do (Thanks L3viathan for the suggestion)

from some_utils.py import add, b
add(3,b)

Answer 4

Where do you want b to come from? Is 5 what you are always going to use? Then put that as the default:

def add(a, b=5):
    ...

Do you want to take the b value you defined in your module along with the function? Import more than just the function:

from some_utils.py import *

Do you want to define b in your other file where you do the import but not pass it to the function? Use a global variable:

def add(a):
    global b
    print(str(a+b))

Answer 5

Functions that are imported only see the variables that they are imported in.

You can use default arguments to bind values from the external module:

some_utils.py:

b = 5
def add(a, b=b):
    return a + b

other script:

from some_utils import add
print(add(4))  # prints 9