'Pop the input source stack.'

def pop_source(self):

    self.instream.close()
    (self.infile, self.instream, self.lineno) = self.filestack.popleft()
    if self.debug:
        print ('shlex:    popping    to    %s,    line    %d' % (self.instream, self.lineno))
    self.state = '    '
