'Skip yielding current node\'s (last yielded node\'s) subtrees.
Examples
>>> from sympy.core import symbols
>>> from sympy.core.basic import preorder_traversal
>>> x, y, z = symbols(\'x y z\')
>>> pt = preorder_traversal((x+y*z)*z)
>>> for i in pt:
...     print(i)
...     if i == x+y*z:
...             pt.skip()
z*(x + y*z)
z
x + y*z'

def skip(self):

    self._skip_flag = True
