def evalPrefix( prefixExpression ):
expressionlist = prefixExpression.split()
expressionstack = Stack()
for element in expressionlist[::-1]:
if element not in '+-*/':
expressionstack.push(element)
else:
num1 = float(expressionstack.pop())
num2 = float(expressionstack.pop())
num = ''
if element == '+':
num = num1 + num2
elif element == '-':
num = num1 - num2
elif element == '*':
num = num1 * num2
elif element == '/':
num = num1 / num2
else:
return None
if num != '':
expressionstack.push(num)
if len(expressionstack) == 1:
return float(expressionstack.pop())
def mystr(anInteger):
NumberStack = Stack()
while anInteger >= 10:
digit = anInteger % 10
NumberStack.push(digit)
anInteger = anInteger // 10
NumberStack.push(anInteger)
aString = ''
for i in range(len(NumberStack)):
aString = aString + chr(NumberStack.pop() + 48)
return aString
