algorithm-in-python/parser/leetcode_examples/calculator.py

import re
from collections import namedtuple
left = r'(?P<LEFT>\()'
right = r'(?P<RIGHT>\))'
var = r'(?P<VAR>[a-z]+)'
num = r'(?P<NUM>\d+)'
add = r'(?P<ADD>\+)'
sub = r'(?P<SUB>\-)'
mul = r'(?P<MUL>\*)'
ws = r'(?P<WS> +)'
pt = re.compile('|'.join([left, right, var, ws, num, add, sub, mul]))

token = namedtuple('token', ['type', 'value'])


def genToken(s):
    scanner = pt.scanner(s)
    for i in iter(scanner.match, None):
        if i.lastgroup != 'WS':
            yield token(i.lastgroup, i.group(0))


class parser(object):
    '''grammar
        expr -> expr {'+'|'-'} term | term
        term -> term '*' item | item
        item -> num | var | '(' expr ')'
    '''

    def __init__(self, s, vars):
        self.token = [i for i in genToken(s)]
        self.lookahead = 0
        self.var = vars

    def parse(self):
        dic = self.term()
        # terminate symbol
        while self.lookahead < len(self.token) and not self.isType('RIGHT'):
            assert self.isType('SUB', 'ADD')
            sign = 1 if self.match() == '+' else -1
            var = self.term()
            for i in var:
                if i in dic:
                    dic[i] += var[i]*sign
                else:
                    dic[i] = var[i]*sign
        return dic

    def match(self, curType=None):
        sym = self.token[self.lookahead]
        # print(sym,curType)
        if curType is None or sym.type == curType:
            self.lookahead += 1
            return sym.value
        raise Exception('Invalid input string')

    def isType(self, *s):
        sym = self.token[self.lookahead]
        return any(sym.type == i for i in s)

    def term(self):
        li = []
        dic = self.item()
        while self.lookahead < len(self.token) and self.isType('MUL'):
            self.match()
            li.append(self.item())
        for d2 in li:
            newDic = {}
            for v1 in dic:
                for v2 in d2:
                    s = ''
                    if v1 == '':
                        s = v2
                    elif v2 == '':
                        s = v1
                    else:
                        s = '*'.join(sorted(v1.split('*')+v2.split('*')))
                    if s in newDic:
                        newDic[s] += dic[v1]*d2[v2]
                    else:
                        newDic[s] = dic[v1]*d2[v2]
            dic = newDic
        return dic

    def item(self):
        if self.isType('NUM'):
            return {'': int(self.match())}
        elif self.isType('VAR'):
            name = self.match()
            if name in self.var:
                return {'': self.var[name]}
            else:
                return {name: 1}
        elif self.isType('LEFT'):
            self.match()
            dic = self.parse()
            self.match('RIGHT')
            return dic
        else:
            print(self.token[self.lookahead])
            raise Exception('invalid string')


class Solution:
    def basicCalculatorIV(self, expression, evalvars, evalints):
        """
        :type expression: str
        :type evalvars: List[str]
        :type evalints: List[int]
        :rtype: List[str]
        """
        self.var = dict(zip(evalvars, evalints))
        dic = parser(expression, self.var).parse()
        n = dic.pop('') if '' in dic else 0
        ret = []
        li = sorted(dic, key=lambda s: (-s.count('*'), s))
        for i in li:
            if dic[i] != 0:
                s = str(dic[i])
                ret.append(s + ('*'+i) if i else s)
        if n != 0:
            ret.append(str(n))
        return ret


if __name__ == '__main__':
    sol = Solution()
    exprs = [
        "((a - b) * (b - c) + (c - a)) * ((a - b) + (b - c) * (c - a))", "e + 8 - a + 5"]
    names = [[], ["e"]]
    vars = [[], [1]]
    for i, j, k in zip(exprs, names, vars):
        print('>>>', i, j, k)
        print(sol.basicCalculatorIV(i, j, k))