title: Merge dataframes of different sizes and multiple columns
body: <p>I have two dataframes that have a like column (part_no). Below are the two dataframes I am starting with and what I would like to end up with. I've tried creating dictionaries to accomplish this and setting the index for both dataframes to the part number but am still struggling. Also, one dataframe has all the needed part numbers and the other is essentially a subset of it.</p>
  
  <p>DF1 (all part numbers are in this dataframe)</p>
  
  <pre><code>+---------+------------+
  | part_no | brake_cost |
  +---------+------------+
  | 1       | 34         |
  +---------+------------+
  | 2       | 513        |
  +---------+------------+
  | 3       | 45         |
  +---------+------------+
  | 4       | 675        |
  +---------+------------+
  | 5       | 345        |
  +---------+------------+
  | 6       | 765        |
  +---------+------------+
  | 7       | 234        |
  +---------+------------+
  </code></pre>
  
  <p>DF2</p>
  
  <pre><code>+---------+------------+
  | part_no | wheel_cost |
  +---------+------------+
  | 2       | 543        |
  +---------+------------+
  | 4       | 234        |
  +---------+------------+
  | 5       | 454        |
  +---------+------------+
  | 7       | 654        |
  +---------+------------+
  </code></pre>
  
  <p>DF3 (What I want to end up with)</p>
  
  <pre><code>+---------+------------+------------+
  | part_no | wheel_cost | brake_cost |
  +---------+------------+------------+
  | 1       | 0          | 34         |
  +---------+------------+------------+
  | 2       | 543        | 513        |
  +---------+------------+------------+
  | 3       | 0          | 45         |
  +---------+------------+------------+
  | 4       | 234        | 675        |
  +---------+------------+------------+
  | 5       | 454        | 345        |
  +---------+------------+------------+
  | 6       |            | 765        |
  +---------+------------+------------+
  | 7       | 654        | 234        |
  +---------+------------+------------+
  </code></pre>