title: Python Pandas - Merge dataFrame on every item in a list
body: <p>Let's say that I have Table 'sales':</p>
  <pre><code>          ProductId   Sales
  0               [1]   $199
  1               [2]   $299
  2         [3, 4, 5]   $399
  3         [6, 7, 8]   $499
  </code></pre>
  <p>and Table 'product':</p>
  <pre><code>        ID            Product
  0       1                   A
  1       2                   B
  2       3                   C
  3       4                   D
  4       5                   E
  5       6                   F
  6       7                   G
  7       8                   H
  </code></pre>
  <p>I want to return a new table 'sales_product'</p>
  <pre><code>            Product   Sales
  0                 A   $199
  1                 B   $299
  2             C,D,E   $399
  3             F,G,H   $499
  </code></pre>
  <p>So it can find all the matched <code>ProductId</code> and return <code>Product</code> value as a comma-joined string in the new table.</p>
  <p>Any Python method can achieve this?</p>