title: Filter pandas dataframe where field is supposedly a timestamp but info() shows non null object
body: <p>I have a dataframe that I am trying to push into a database but I get an error message that my primary key constraint is violated:</p>
  
  <pre><code>ecom.to_sql('ecom',
              con = engine,
              schema = 'ga_shop',
              index = False,
              if_exists = 'append')
  sqlalchemy.exc.IntegrityError: (psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "ecom_pk"
  DETAIL:  Key (product_name, dimension3, dimension1)=(Apples, 2019-10-29 19:12:58.83+00, 1572376787423.pgp5jcd7) already exists.
  </code></pre>
  
  <p>I would like to filter dataframe ecom to take a look at these duplicate rows but I am unable to:</p>
  
  <pre><code>ecom[(ecom['dimension3'] == '2019-10-29 19:12:58.83+00')]
  </code></pre>
  
  <p>Returns an empty dataframe.</p>
  
  <pre><code>ecom.info()
  &lt;class 'pandas.core.frame.DataFrame'&gt;
  Int64Index: 82 entries, 14014 to 15002
  Data columns (total 15 columns):
  dimension1                   82 non-null object
  dimension3                   82 non-null object
  product_name                 82 non-null object
  
  ecom.head()
                dimension1                     dimension3  ... item_revenue sampling
  0  1572337407387.0epe8tn  2019-10-29T04:20:08.119-04:00  ...          0.0    False
  1  1572337407387.0epe8tn  2019-10-29T04:20:08.119-04:00  ...          0.0    False
  2  1572337407387.0epe8tn  2019-10-29T04:20:08.119-04:00  ...          0.0    False
  3  1572337407387.0epe8tn  2019-10-29T04:20:08.119-04:00  ...          0.0    False
  4  1572337407387.0epe8tn  2019-10-29T04:20:08.119-04:00  ...          0.0    False
  </code></pre>
  
  <p>Field dimension3 is an iso timestamp that I retreived from an API but it's unclear to me how pandas is storing it since it says '82 non null object' when I check with <code>ecom.info()</code></p>
  
  <p>How can I filter on dimension3, the timestamp, to match that of the error message so that I can see those duplicates?</p>