Example:

$ cat foo.py
import bar
bar.baz
$ cat bar.py
import foo
baz = 2
$ ./python foo.py 
Traceback (most recent call last):
  File "foo.py", line 1, in <module>
    import bar
  File "/home/serhiy/py/cpython/bar.py", line 1, in <module>
    import foo
  File "/home/serhiy/py/cpython/foo.py", line 2, in <module>
    bar.baz
AttributeError: module 'bar' has no attribute 'baz'

Patched:

$ ./python foo.py 
Traceback (most recent call last):
  File "foo.py", line 1, in <module>
    import bar
  File "/home/serhiy/py/cpython/bar.py", line 1, in <module>
    import foo
  File "/home/serhiy/py/cpython/foo.py", line 2, in <module>
    bar.baz
AttributeError: partially initialized module 'bar' has no attribute 'baz' (most likely due to a circular import)