'Collapse self.body to a single string; replace it and return it.'

def collapse_body(self):

    if isinstance(self.body, basestring):
        return self.body
    newbody = []
    for chunk in self.body:
        if (py3k and (not isinstance(chunk, bytes))):
            raise TypeError(("Chunk    %s    is    not    of    type    'bytes'." % repr(chunk)))
        newbody.append(chunk)
    newbody = ntob('').join(newbody)
    self.body = newbody
    return newbody
