code: def truncate_file(f):
      
      if isinstance(f, InMemoryUploadedFile):
          f.file = StringIO()
      else:
          f.seek(0)
          f.truncate(0)
docs: Clear uploaded file and allow write to it.
      Only for not too big files!!!
      Also can clear simple opened file.
      Examples:
          truncate_file(request.FILES['file'])
  
          with open('/tmp/file', 'rb+') as f:
              truncate_file(f)