Python – ImportError: Cannot import name X

I have four different files named: main.py, vector.py, entity.py and physics.py. I will not post all the code, just the imports, because I think that's where the error is (If you want, I can post more).

main.py:

import time
from entity import Ent
from vector import Vect
#the rest just creates an entity and prints the result of movement

entity.py:

from vector import Vect
from physics import Physics
class Ent:
    #holds vector information and id
def tick(self, dt):
    #this is where physics changes the velocity and position vectors

vector.py:

from math import *
class Vect:
    #holds i, j, k, and does vector math

physics.py:

from entity import Ent
class Physics:
    #physics class gets an entity and does physics calculations on it.

I then run from main.py and I get the following error:

Traceback (most recent call last):
File "main.py", line 2, in <module>
    from entity import Ent
File ".../entity.py", line 5, in <module>
    from physics import Physics
File ".../physics.py", line 2, in <module>
    from entity import Ent
ImportError: cannot import name Ent

I'm guessing that the error is due to importing entity twice, once in main.py, and later in physics.py, but I don't know a workaround. Can anyone help?