part 3 pandas issue

Finished up pt 3 with Farnam: 

1. some issues with "Applying a Function" in Step 3. certain Pandas versions seem to have issues with making a new column in this way: 
`df['above_poverty_line'] = df['poverty_level'].apply(assign_level)`. need to use `.loc`

2. might be useful to add more reinforcement about the difference between attributes and methods, e.g., why `df.shape` vs. `df.info()`