No module named selenium

i'm on mac and when i click on mac_start.command i get this

```
Starting InstaPy with quickstart
====================
Traceback (most recent call last):
File "../quickstart.py", line 2, in
from instapy import InstaPy
File "/Library/Python/2.7/site-packages/instagram_py-0.0.1-py2.7.egg/instapy/__init__.py", line 3, in
from .instapy import InstaPy
File "/Library/Python/2.7/site-packages/instagram_py-0.0.1-py2.7.egg/instapy/instapy.py", line 13, in
from selenium import webdriver
ImportError: No module named selenium
logout
Saving session...
...copying shared history...
...saving history...truncating history files...
...completed.

[Process completed]
```
any help?