title: Django form validation, clean(), and file upload
body: <p>Can someone illuminate me as to exactly when an uploaded file is actually written to the location returned by "upload_to" in the FileField, in particular with regards to the order of field, model, and form validation and cleaning?</p>
  
  <p>Right now I have a "clean" method on my model which assumes the uploaded file is in place, so it can do some validation on it.  It looks like the file isn't yet saved, and may just be held in a temporary location or in memory.  If that is the case, how do I "open" it or find a path to it if I need to execute some external process/program to validate the file?</p>
  
  <p>Thanks,</p>
  
  <p>Ian</p>