def trans_infix_suffix(line):
st = SStack()
exp = []
for x in tokens(line): # tokens是一个待定义的生成器
if x not in infix_operators: # 运算对象直接送出
exp.append(x)
elif st.is_empty() or x == '(': # 左括号进栈
st.push(x)
elif x == ')': # 处理右括号的分支
while not st.is_empty() and st.top() != '(':
exp.append(st.pop())
if st.is_empty(): # 没有找到左括号，就是不配对
raise SyntaxError('Missing "(".')
st.pop() # 弹出左括号，右括号也不进栈
else: # 处理运算符，运算符都看作左结合
while (not st.is_empty()) and priority[st.top()] >= priority[x]:
exp.append(st.pop())
st.push(x) # 算数运算符进栈
while not st.is_empty(): # 送出栈里剩下的运算符
if st.pop() == '(': # 如果还有左括号，就是不配对
raise SyntaxError('Extra "(".')
exp.append(st.pop())
return exp
def postorder_nonrec(t_, proc):
s = SStack()
while t_ is not None or not s.is_empty():
while t_ is not None: # 下行循环，直到栈顶的两个树空
s.push(t_)
t_ = t_.left if t_.left is not None else t_.right # 注意这个条件表达式的意义：能左就左，否则向右一步
t_ = s.pop() # 栈顶是访问结点
proc(t_.dat)
if not s.is_empty() and s.top().left == t_:
t_ = s.top().right # 栈不空且当前结点是栈顶的左子结点
else:
t_ = None # 没有右子树或右子树遍历完毕，强迫退栈
def postorder_nonrec(t, proc):
s = SStack()
while t is not None or not s.is_empty():
while t is not None: #下行循环，直到栈顶的两子树空
s.push(t)
t = t.left if t.left is not None else t.right #能左就左否则向右
t = s.pop() #栈顶是应访问节点
proc(t.data)
if not s.is_empty() and s.top().left == t:
t = s.top().right #栈不空且当前节点是栈定左子节点
else: #没有右子树或右子树遍历完毕，强迫退栈
t = None
def dfs_non_recursive_traverse_postorder(t, proc): #dfs非递归 后根序
s = SStack()
while t is not None or not s.is_empty():
while t is not None:
s.push(t)
if t.left is not None:
t = t.left
else:
t = t.right
t = s.pop()
proc(t.data)
if not s.is_empty() and s.top().left == t:
t = s.top().right #这一步很关键
else:
t = None