title: file download from google drive to colaboratory
body: <p>I was trying to download file from my google drive to colaboratory.</p>
  
  <pre><code>file_id = '1uBtlaggVyWshwcyP6kEI-y_W3P8D26sz'
  
  import io
  from googleapiclient.http import MediaIoBaseDownload
  
  request = drive_service.files().get_media(fileId=file_id)
  downloaded = io.BytesIO()
  downloader = MediaIoBaseDownload(downloaded, request)
  done = False
  while done is False:
    # _ is a placeholder for a progress object that we ignore.
    # (Our file is small, so we skip reporting progress.)
    _, done = downloader.next_chunk()
  
  downloaded.seek(0)
  print('Downloaded file contents are: {}'.format(downloaded.read()))
  </code></pre>
  
  <p>doing so am getting this error:</p>
  
  <pre><code>NameError: name 'drive_service' is not defined
  </code></pre>
  
  <p>How to remove this error?</p>