title: `TypeError: invalid type promotion` when appending to a heterogeneous numpy array
body: <p>I have created an array with:</p>
  
  <pre><code>Ticket_data = np.empty((0,7),
                         dtype='str,datetime64[m],datetime64[m],str,str,str,str')
  </code></pre>
  
  <p>and I am trying to append data with:</p>
  
  <pre><code>lineitem = [str(data[0][0]), OpenDT, CloseDT, str(data[0][11]),
              str(data[0][12]), str(data[0][13]), str(data[0][14])]
  </code></pre>
  
  <p>Where <code>OpenDT</code> and <code>CloseDT</code> were created with <code>np.datetime64(DTstring, 'm')</code></p>
  
  <p>I am getting the error: </p>
  
  <pre><code>Traceback (most recent call last):
    File "Daily Report.py", line 25, in &lt;module&gt;
      np.append(Ticket_data, np.array([lineitem]), axis=0)
    File "C:\Python27\lib\site-packages\numpy\lib\function_base.py", line 3884, in append
      return concatenate((arr, values), axis=axis)
  TypeError: invalid type promotion
  </code></pre>
  
  <hr>
  
  <p>Edit:</p>
  
  <pre><code>print np.array([lineitem])
  </code></pre>
  
  <p>outputs</p>
  
  <pre><code>[['21539' '2015-06-30T10:46-0700' '2015-06-30T10:55-0700' 'Testtext'
   'Testtext2' 'Testtext3' 'Testtext5']]
  </code></pre>
  
  <p>and</p>
  
  <pre><code>print np.array([lineitem], dtype=Ticket_data.dtype)
  </code></pre>
  
  <p>Outputs</p>
  
  <pre><code>[[('', 245672259890L, datetime.datetime(1970, 1, 1, 0, 0), '', '', '', '')
    ('', datetime.datetime(2015, 6, 30, 17, 46), datetime.datetime(1970, 1, 1, 0, 0), '', '', '', '')
    ('', datetime.datetime(2015, 6, 30, 17, 55), datetime.datetime(1970, 1, 1, 0, 0), '', '', '', '')
    ('', 7741528753124368710L, datetime.datetime(1982, 11, 21, 6, 33), '', '', '', '')
    ('', 7959953343691844691L, datetime.datetime(1970, 1, 1, 0, 0), '', '', '', '')
    ('', datetime.datetime(5205, 7, 21, 7, 42), datetime.datetime(1970, 1, 1, 0, 0), '', '', '', '')
    ('', 2336635297857499728L, 2338042681633169744L, '', '', '', '')]]
  </code></pre>
  
  <p>What can I do to resolve this?</p>