title: pandas - convert a column with multiple date formats to datetime
body: <p>I have a column in a dataframe with multiple date formats that need to be converted to datetime.</p>
  
  <pre><code>date              amount
  September 2018    15
  Sep-18            20
  </code></pre>
  
  <p>The output should look like</p>
  
  <pre><code>date              amount
  2018-09-01        15
  2018-09-01        20
  </code></pre>
  
  <p>Using pd.to_datetime(df['Month']) returns the error...</p>
  
  <p>OutOfBoundsDatetime: Out of bounds nanosecond timestamp: 1-09-18 00:00:00</p>