Copy the content of a docx inside another in python app engine

gistfile1.py

from server.api.drive import Drive
from server.libs.docx import Document
from cStringIO import StringIO

driveFile = Drive.getFile('DRIVE_ID')
doc = Document(StringIO(Drive.downloadFile(driveFile['downloadUrl'])))
doc_to_copy = Document(StringIO(Drive.downloadFile(Drive.getFile('DRIVE_ID_TO_COPY')['downloadUrl'])))

for element in doc_to_copy._body._element:
    doc._body._element.append(element)

output = StringIO()
doc.save(output)

Drive.uploadFile('test-result.docx',
                 driveFile.get('mimeType'),
                 output,
                 None,
                 False,
                 'owner.email@google.com')