def prepend(self, cmd, kind):
        if type(cmd) is not type(''):
            raise TypeError, \
                  'Template.prepend: cmd must be a string'
        if kind not in stepkinds:
            raise ValueError, \
                  'Template.prepend: bad kind %r' % (kind,)
        if kind == SINK:
            raise ValueError, \
                  'Template.prepend: SINK can only be appended'
        if self.steps and self.steps[0][1] == SOURCE:
            raise ValueError, \
                  'Template.prepend: already begins with SOURCE'
        if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
            raise ValueError, \
                  'Template.prepend: missing $IN in cmd'
        if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
            raise ValueError, \
                  'Template.prepend: missing $OUT in cmd'
        self.steps.insert(0, (cmd, kind))
t.prepend(cmd, kind) adds a new step at the front.
dataset/ETHPy150Open azoft-dev-team/imagrium/env/Lib/pipes.py/Template.prepend