title: dataframe should contain multiple rows, but always contain a single row after appending
body: <p>in this code, matrixdf should contain a big dataset because, i am appending matrixdf2, a single row in the dataframe. but after simulation, i have observed, it's still a single row.  what can be the problem here. at first i initialized, then the loop started.</p>
  <pre><code>def distance_count(self):
    m = self.client.distance_matrix(self.origins, self.destinations)
    matrixdf = json_normalize(m,['rows','elements']) 
    print(&quot;init print&quot;)
    print(matrixdf)
    next_time = time.time()
    for i in range(5):
     matrix = self.client.distance_matrix(self.origins, self.destinations)
     matrixdf2 = json_normalize(matrix,['rows','elements'])
     print(&quot;row1&quot;)
     print(matrixdf2)
     matrixdf.append(matrixdf2)
     print(&quot;full&quot;)
     print(matrixdf)
     i = i + 5
     next_time += i
     time.sleep(max(0, next_time - time.time()))
    matrixdf.to_csv('dataset.csv')
    files.download('dataset.csv')
   
  </code></pre>