def infix_to_suffix(expr):
""" 从中序表达式到后序表达式的转换 """
stack, suffixes, operators = Stack(), [], {
'*': 3,
'/': 3,
'+': 2,
'-': 2,
'(': 1,
')': 1,
}
for i in list(expr.replace(' ', '')):
if i.upper() in string.ascii_uppercase:
suffixes.append(i)
elif i == '(':
stack.push(i)
elif i == ')':
top = stack.pop()
while top != '(':
suffixes.append(top)
top = stack.pop()
else:
while not stack.isEmpty() and operators[
stack.peek()] >= operators[i]:
suffixes.append(stack.pop())
stack.push(i)
while not stack.isEmpty():
suffixes.append(stack.pop())
return ''.join(suffixes)
class StackTestCase(unittest.TestCase):
""" 测试 stack.py """
def setUp(self) -> None:
self.stack = Stack()
def testStackIsEmpty(self) -> None:
self.assertTrue(self.stack.isEmpty())
self.stack.push(1)
self.assertFalse(self.stack.isEmpty())
def testStackPush(self) -> None:
self.stack.push(1)
self.assertEqual([1], self.stack.items)
self.stack.push('a')
self.assertEqual([1, 'a'], self.stack.items)
self.stack.push(False)
self.assertEqual([1, 'a', False], self.stack.items)
def testStackPop(self):
self.stack.push(1)
self.stack.push('a')
self.stack.push(False)
self.stack.push(None)
self.stack.pop()
self.assertEqual([1, 'a', False], self.stack.items)
self.stack.pop()
self.assertEqual([1, 'a'], self.stack.items)
self.stack.pop()
self.assertEqual([1], self.stack.items)
self.stack.pop()
self.assertEqual([], self.stack.items)
def testStackPeek(self) -> None:
self.stack.push(1)
self.assertEqual(1, self.stack.peek())
self.stack.push('a')
self.assertEqual('a', self.stack.peek())
self.stack.push(True)
self.assertEqual(True, self.stack.peek())
self.stack.push(None)
self.assertEqual(None, self.stack.peek())
def testStackSize(self) -> None:
self.stack.push(99)
self.assertEqual(1, self.stack.size())
self.stack.push('A')
self.assertEqual(2, self.stack.size())
self.stack.push(True)
self.assertEqual(3, self.stack.size())
self.stack.push(None)
self.assertEqual(4, self.stack.size())
def tearDown(self) -> None:
del self.stack