Programming Praxis, RPN
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import sys | |
class RPN(object): | |
def __init__(self): | |
self._stack = [] | |
self._expr = '' | |
self._operators = '+-*/' | |
def read_expr(self, out=sys.stdout): | |
self._expr = raw_input('? ') | |
out.write('{0:.4f}'.format(self.process_expr()) + "\n") | |
def process_expr(self): | |
tokens = self._expr.split() | |
for token in tokens: | |
if token not in self._operators: | |
self._stack.append(token) | |
else: | |
if len(self._stack) < 2: | |
print "Too few operands" | |
else: | |
op1 = self._stack.pop() | |
op2 = self._stack.pop() | |
self._stack.append(str(eval(op2 + token + op1))) | |
return float(self._stack[-1]) | |
if __name__ == '__main__': | |
rpn = RPN() | |
while True: | |
rpn.read_expr() |
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