title: openpyxl load_workbook from backend service
body: <p>I have some openpyxl code in my backend service (google app engine) and I'd like to load a file from google cloud store / blobstore, but passing the file stream (via blobstore reader) doesn't appear to be valid for load_workbook. xlrd has an option to pass file contents (<a href="https://stackoverflow.com/questions/31380301/reading-contents-of-excel-file-in-python-webapp2">Reading contents of excel file in python webapp2</a>). Is there something similar for openpyxl?</p>
  
  <pre><code>blobstore_filename = '/gs{}'.format('/mybucket/mycloudstorefilename.xlsx')
  blob_key = blobstore.create_gs_key(blobstore_filename)
  blob_reader = blobstore.BlobReader(blob_key)
  blob_reader = blobstore.BlobReader(blob_key, buffer_size=1048576)
  blob_reader = blobstore.BlobReader(blob_key, position=0)
  blob_reader_data = blob_reader.read()
  load_workbook(blob_reader_data)
  </code></pre>
  
  <p>The error is:
  UnicodeDecodeError
  'ascii' codec can't decode byte 0x9d in position 11: ordinal not in range(128)</p>