'Substitute terms in the tree
>>> from blaze.expr import symbol
>>> t = symbol(\'t\', \'var * {name: string, amount: int, id: int}\')
>>> expr = t.amount + 3
>>> expr._subs({3: 4, \'amount\': \'id\'}).isidentical(t.id + 4)
True'

def _subs(self, d):

    return subs(self, d)
