基于python的单位正整数四则运算表达式求值

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版本2

#!/usr/bin/env python# -*- coding:utf-8 -*-# Filename:test_expr.pyimport unittestfrom expr import *class ExprTestCase(unittest.TestCase):    def setUp(self):        return    def tearDown(self):        return    def test_num_index0(self):        self.assertEqual(1, num("1", 0))        self.assertEqual(2, num("2+3", 0))    def test_num_index2(self):        self.assertEqual(3, num("2+3", 2))    def test_add(self):        self.assertEqual(2, add("1+1"))        self.assertEqual(3, add("1+2"))    def test_add3(self):        self.assertEqual(6, add("1+2+3"))        def test_minus(self):        self.assertEqual(1, minus("2-1"))        self.assertEqual(0, minus("2-1-1"))    def test_mul(self):        self.assertEqual(6, mul("2*3"))        self.assertEqual(24, mul("2*3*4"))    def test_div(self):        self.assertEqual(2, div("6/3"))        self.assertEqual(1, div("9/3/3"))    def test_mix(self):        self.assertEqual(7, mix(1+2*3))if __name__ == '__main__':    unittest.main()

def num(s, pos):    return int(s[pos])def add(s):    return chains(s)def minus(s):    return chains(s)def mul(s):    return chains(s)def div(s):    return chains(s)def apply_mix(val, s, pos):    if s[pos] == '+':        val += num(s, pos + 1)    elif s[pos] == '-':        val -= num(s, pos + 1)      if s[pos] == '*':        val *= num(s, pos + 1)      elif s[pos] == '/':        val /=  num(s, pos + 1)    return valdef chains(s):    val = num(s, 0)    for i in range(1, len(s)):        val = apply_mix(val, s, i)    return valdef mix(s):    return add(mul(s))

版本1

#!/usr/bin/env python# -*- coding:utf-8 -*-# Filename:test_expr.pyimport unittestfrom expr import *class ExprTestCase(unittest.TestCase):    def setUp(self):        return    def tearDown(self):        return    def test_num_index0(self):        self.assertEqual(1, num("1", 0))        self.assertEqual(2, num("2+3", 0))    def test_num_index2(self):        self.assertEqual(3, num("2+3", 2))    def test_add(self):        self.assertEqual(2, add("1+1"))        self.assertEqual(3, add("1+2"))    def test_add3(self):        self.assertEqual(6, add("1+2+3"))        def test_minus(self):        self.assertEqual(1, minus("2-1"))        self.assertEqual(0, minus("2-1-1"))    def test_add_minus(self):        self.assertEqual(4, add_minus("3+2-1"))if __name__ == '__main__':    unittest.main()

def num(s, pos):    return int(s[pos])def add(s):    return add_minus(s)def minus(s):    return add_minus(s)def add_minus(s):    val = num(s, 0)    for i in range(1, len(s)):        if s[i] == '+':            val += num(s, i + 1)        elif s[i] == '-':            val -= num(s, i + 1)    return val

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# num, plus, minus, mul, div# num('1') --># plus('1','2') --> plus(num('1'), num('2'))def extract(notation):    if len(notation) == 2:        return (notation[0], notation[1], None)    elif len(notation) == 3:        return (notation[0], notation[1], notation[2])def expr(notation):    op, n1, n2 = extract(notation)    if op == 'num':        return do_num(n1)    elif op == '+':        return do_add(n1, n2)    elif op == '-':        return do_minus(n1, n2)    elif op == '*':        return do_mul(n1, n2)'''  expr(num('1'))    case 'num'        do_num'''        def num(n):    return ('num', n)def plus(n1, n2):    return ('+', n1, n2)def minus(n1, n2):    return ('-', n1, n2)def mul(n1, n2):    return ('*', n1, n2)def do_num(n1):    return int(n1)def do_add(n1, n2):    return expr(n1) + expr(n2)def do_minus(n1, n2):    return expr(n1) - expr(n2)def do_mul(n1, n2):    return expr(n1) * expr(n2)    # 1n1 = num('1')assert(1 == expr(n1))# 1+2n1 = num('1')n2 = num('2')assert(3 == expr(plus(n1, n2)))# 1+2+3n1 = num('1')n2 = num('2')n3 = plus(n1, n2)n4 = num('3')assert(6 == expr(plus(n3, n4)))# 3-2n1 = num('3')n2 = num('2')assert(1 == expr(minus(n1, n2)))# 1+2-3n1 = num('1')n2 = num('2')n3 = plus(n1, n2)n4 = num('3')assert(0 == expr(minus(n3, n4)))# 1*2n1 = num('3')n2 = num('2')assert(6 == expr(mul(n1, n2)))