Update the contents and set the hash and modification time

def update_contents(self, contents, mime_type):
        """Update the contents and set the hash and modification time"""
        import hashlib
        import time

        new_size = len(contents)

        self.mime_type = mime_type

        if mime_type == 'text/plain':
            self.contents = contents.encode('utf-8')
        else:
            self.contents = contents

        old_hash = self.hash

        self.hash = hashlib.md5(self.contents).hexdigest()

        if self.size and (old_hash != self.hash):
            self.modified = int(time.time())

        self.size = new_size