ModuleNotFoundError when running code, but works in ipython

Question

I'm trying to use the BitVector library in python 3.6. When I run ipython and run "from BitVector import BitVector", I get no error and can successfully use BitVector. However, when I try to run my actual code that contains "from BitVector import BitVector", I get the error:

Traceback (most recent call last):
    File "testharness.py", line 1, in <module>
      from BitVector import BitVector
ModuleNotFoundError: No module named 'BitVector'

I installed BitVector using "pip3 install BitVector"