Rachel

These are my edits to lab 1. I tried to make the lab more consistent and slightly shorter (based on feedback from students). Here are the big changes:
1. I made some of the online resources "required reading" and deleted corresponding sections of the lab because I found the online resources clearer. 
2. I deleted a few homework exercises that were ambiguous (also with the goal of making the lab slightly shorter).
3. I deleted most (not all!) text and exercises about mutable vs. immutable objects because I felt this topic was unduly emphasized. I think this is an (important) detail that most students will not be able to absorb in their first exposure to Python.
4. I added some other strategies to the section "Learning Python."