# rpncalc3.py
operands = []
def isOperand(token):
try:
float(token)
return True
except ValueError:
return False
def printOperands():
print(operands)
def popOperands(n):
size = len(operands)
if size >= n:
result = operands[size - n : size]
global operands
operands = operands[0 : size - n]
return result
else:
return None
def pushOperand(operand):
operands.append(operand)
def plus():
ops = popOperands(2)
if not (ops is None):
pushOperand(ops[0] + ops[1])
def minus():
ops = popOperands(2)
if not (ops is None):
pushOperand(ops[0] - ops[1])
# the functions above handles all access to the operand stack
# the code below has no references to the operand stack, only to the functions above
def main():
while (True):
printOperands()
token = raw_input(" > ")
if isOperand(token):
operand = float(token)
pushOperand(operand)
elif token == "exit":
break
elif token == "+":
plus()
elif token == "-":
minus()
else:
print("Unsupported operator: " + token)
print("program exited")
main() | 