我不得不编写一个使用后缀表示法的Stack类来计算使用Python从文本文件输入的问题。我也想更新列表，不允许任何时候有超过10个项目。我相信，我的推送或流行方法似乎有些问题。任何建议都将不胜感激，谢谢。
更新了书面代码：
class Stack:
#initializing the data
def __init__(self):
self.__data = [None] * 10
self.__length = 0
#destroying the existing stack
def __destroy__(self):
self.__data = [None] * 10
self.__length = 0
return
#checking to see if the stack is empty
def is_stack_empty(self):
return self.__length == 0
#checking to see if the stack is full
def is_stack_full(self):
if self.__length == 10:
return True
else:
return False
#pushing an item to the stack
def push(self, item):
try:
self.__data.append(item)
self.__length = self.__length + 1
return
except IndexError:
print("ERROR: Cannot push more than 10 items to the stack.")
#popping an item from the stack
def pop(self):
try:
return self.__data.pop()
self.__length = self.__length - 1
return
except IndexError:
print("ERROR: Cannot pop from an empty list.")
#checking to see what the last item on the stack is
def top(self):
return self.__data[-1]
#checking the length of the stack
def __len__(self):
return self.__length
#overloading the string operator
def __str__(self):
return str(self.__data)
def main():
file_name = input("Enter the name of the file containing postfix expressions: ")
#expression = input("Enter a mathmatical expression: ")
#e_list = expression.split()
#validates file
found = False
while not found:
try:
in_file = open(file_name)
found = True
except Exception as ex:
print(file_name, " is not found.")
file_name = input("Please re-enter a valid text file name: ")
stack = Stack()
for each in in_file:
try:
value = int(each)
except Exception as ex:
second = stack.pop()
first = stack.pop()
if each == "+":
try:
answer = first + second
stack.push(answer)
except Exception as ex:
print("ERROR: "+ expression + " is an invalid postfix expression.")
elif each == "-":
try:
answer = first - second
stack.push(answer)
except Exception as ex:
print("ERROR: "+ expression + " is an invalid postfix expression.")
elif each == "*":
try:
answer = first * second
stack.push(answer)
except Exception as ex:
print("ERROR: "+ expression + " is an invalid postfix expression.")
elif each == "/":
try:
answer = first / second
stack.push(answer)
except Exception as ex:
print("ERROR: "+ expression + " is an invalid postfix expression.")
else:
stack.push(value)
print("Answer: ", stack.pop())
return
main()
文件内容：
5 10 * 6 +
20 5 /
3 8 6 + *
3 4 + 9 - 12 +
9 3 2 1 + + /
3 + 5
* 3 4 5 + *
4 9 1 3 + -
h 3 +
0 1 2 3 4 5 6 7 8 9 10 11 12 + / - * + + + + + * * /
结果输出：
Enter the name of the file containing postfix expressions: expressions.txt
Expression: 5 10 * 6 +
Answer: 56
Expression: 20 5 /
Answer: 4.0
Expression: 3 8 6 + *
Answer: 42
Expression: 3 4 + 9 - 12 +
Answer: 10
Expression: 9 3 2 1 + + /
Answer: 1.5
ERROR: 3 + 5
is an invalid postfix expression.
Expression: 3 + 5
Answer: 5
ERROR: * 3 4 5 + *
is an invalid postfix expression.
Expression: * 3 4 5 + *
Answer: 27
Expression: 4 9 1 3 + -
Answer: 5
ERROR: h 3 +
is an invalid postfix expression.
Expression: h 3 +
Answer: None
Expression: 0 1 2 3 4 5 6 7 8 9 10 11 12 + / - * + + + + + * * /
Answer: 0.0
预期产出：
Enter the name of the file containing postfix expressions: expressions.txt
Expression: 5 10 * 6 +
Answer: 56
Expression: 20 5 /
Answer: 4.0
Expression: 3 8 6 + *
Answer: 42
Expression: 3 4 + 9 - 12 +
Answer: 10
Expression: 9 3 2 1 + + /
Answer: 1.5
ERROR: 3 + 5 is an invalid postfix expression
ERROR: * 3 4 5 + * is an invalid postfix expression
ERROR: 4 9 1 3 + - is an invalid postfix expression
ERROR: h 3 + is an invalid postfix expression
ERROR: 0 1 2 3 4 5 6 7 8 9 10 11 12 + / - * + + + + + * * / is an invalid postfix expression
答案 0 :(得分：0)
您将e_list替换为in_file，但它们不是一回事：前者是一个符号列表，如['5', '10', '*', '6', '+']，而后者是一个文件的迭代器，所以现在每个都是5 10 * 6 +，而不是字符串中的单个元素。
for expression in in_file:
e_list = expression.split()
for each in e_list:
try:
value = int(each)
except ValueError as ex:
second = stack.pop()
first = stack.pop()
# ...
答案 1 :(得分：0)
您的输入格式是一个行流，每个行都是由空格分隔的标记流组成一个表达式，如下所示：
5 10 * 6 +
20 5 /
但是您的代码会尝试将每一行视为一个令牌：
for each in in_file:
try:
value = int(each)
这里需要一个嵌套循环，内部循环在空格上分割，以按预期处理每一行的每个标记：
for line in in_file:
for token in line.split():
目前尚不清楚是否应该为每个新行重置堆栈。如果是，您需要为每一行创建一个新的Stack：
for line in in_file:
stack = Stack()
for token in line.split():
...或destroy每行末尾的堆栈，以便您可以重复使用它：
stack = Stack()
for line in in_file:
for token in line.split():
# etc.
stack.__destroy__()
此外，您的Stack课程还有一个需要解决的严重问题。您的一些方法（__init__，is_stack_full，）使用__data作为10个元素的固定大小的列表，并使用单独的__length来告诉您这些元素中有多少个是有效值，而其他人（__destroy__，is_stack_empty，top，__len__，__str__）使用__data作为0-10个元素的列表这些都是有效的，而其他人（push，pop）在同一方法中混淆了两者。您必须选择一个设计或另一个设计，并使用错误的方法修复方法。
作为一个小问题：您的__destroy__方法是由主代码调用的公共方法，而不是__init__之类的Python协议的实现，因此它应该被命名为destroy 。您的__data属性是常规的“按惯例”私有值，而不是您需要从超类和/或子类中隐藏以避免意外冲突的值，因此它应该是_data。
当然，您的代码中可能存在其他错误，但这应该足以让您超越当前的障碍（以及您未预料到的下一个障碍）。