Usually circular imports are fine. Not great maybe, but ok. This pair of tiny files demonstrates how prematurely using a value is where the problem really manifests.

a.py

import b

# print(b.val)

"""
If left commented, this pair of module is perfectly fine, no exceptions are raised.

If uncommented, you'll see a stack trace like:

Traceback (most recent call last):
  File "a.py", line 2, in <module>
    import b
  File "/home/mahmoud/tmp/b.py", line 2, in <module>
    import a
  File "/home/mahmoud/tmp/a.py", line 4, in <module>
    print(b.val)
AttributeError: 'module' object has no attribute 'val'

The module was created, but the value wasn't populated yet. The same would happen if you do

from b import val

The problem with that statement isn't the b import, but the val import.
"""

b.py

import a

val = 'test'