OPERATORS = {'+': (1, lambda x, y: x + y), '-': (1, lambda x, y: x - y),
             '*': (2, lambda x, y: x * y), '/': (2, lambda x, y: x / y),
             'unary_minus': (3, lambda x: -1*x),}

def parse(line):
    num = ''
    for symbol in line:
        if symbol in OPERATORS or symbol in '()':
            if num:
                yield float(num)
                yield symbol
                num=''
            else:
                if symbol=='-':
                    yield 'unary_minus'
                else:
                    yield symbol
        else:
            num+=symbol
    if num:
        yield float(num)

def sort(parsed):
    tmp = []
    for i in parsed:
        if i in OPERATORS:
            while tmp and tmp[-1] != '(' and OPERATORS[i][0] <= OPERATORS[tmp[-1]][0]:
                yield tmp.pop()
            tmp.append(i)
        elif i == ')':
            while tmp:
                x = tmp.pop()
                if x == '(':
                    break
                yield x
        elif i == '(':
            tmp.append(i)
        else:
            yield i
    while tmp:
        yield tmp.pop()

def calc(sort):
    tmp = []
    for i in sort:
        if i in OPERATORS:
            if i=='unary_minus':
                x = tmp.pop()
                tmp.append(OPERATORS[i][1](x))
            else:
                y = tmp.pop()
                x = tmp.pop()
                tmp.append(OPERATORS[i][1](x, y))
        else:
            tmp.append(i)
    return tmp[0]

for formula in ['2+2*2','-(4+10)/2','10-(2*5)']:
    print formula,'= ', calc(sort(parse(formula)))
    pass

for formula in ['-(4+10)/2','10-(2*5)','-2+10','10+(-2*5)']:
    #print formula,'= ', list(parse(formula)), ', '#,list(sort(parse(formula)))
    pass
    print formula,'= ', calc(sort(parse(formula)))