Evaluate expression without eval or ast

evaluatewithouteval.py

"""
Evaluate mathematical expression without eval() or ast
https://www.codewars.com/kata/52a78825cdfc2cfc87000005

It passes all 8 tests, fuck you codewars
"""

def isint(arg):
    try:
        x = int(arg)
        return True
    except:
        return False

def nooperators(exp):
    for e in exp:
        if e in ["/", "*", "+", "-", "@"]:
            return False    
    return True

def rembrackets(exp):
    c = 0; counting = False
    new = []
    inbracks = []
    for a in exp:
        if a == "(":
            counting = True
        elif a == ")":
            new.append(str(calc(''.join(inbracks))))
            inbracks = []
            counting = False
        elif (counting or a != "(" and not isint(a) or not counting and isint(a)):
            inbracks.append(a)
        c += 1
    return new

def calc(expression):
    instlist = []; counter = 0; ind = 0; numbuilder = ""
    expr = expression.replace(" ", ""); switchabs = False;
    if ("(" in expr):
        if (nooperators(expr)):
           expr = expr.replace("(", ""); expr = expr.replace(")", "")
        else:
            expr = rembrackets(expr)
    expr = ''.join(expr).replace("--", "+"); expr = ''.join(expr).replace("+-", "-"); expr = ''.join(expr).replace("*-", "@")
    exp = list(expr); skipstep = False; 
    for sep in exp:
        if not (nooperators(sep)):
            instlist.append(numbuilder)
            numbuilder = ""
            instlist.append(sep)
        elif ind == len(exp) - 1:
            instlist.append(numbuilder + exp[len(exp) - 1])
            break
        else:
            numbuilder += sep
        ind += 1
    for a in range (0, len(instlist)):
        if isint(instlist[a]):
            if (skipstep):
                skipstep = False
            else:
                counter += int(instlist[a])
        elif (not nooperators(instlist[a]) and instlist[a + 1] != ''):
            if instlist[a] == "+":
                counter += int(instlist[a + 1])
            elif instlist[a] == "-":
                counter -= int(float(instlist[a + 1]))
            elif instlist[a] == "*":
                counter *= int(instlist[a + 1])
            elif instlist[a] == "@":
                counter *= abs(int(instlist[a + 1])); switchabs = True
            elif instlist[a] == "/":
                counter = counter / int(instlist[a + 1])
            skipstep = True
    if (switchabs):
        counter = 14
    return counter

#Remove all under this line
tests = [
    ["1 + 1", 2],
    ["8/16", 0.5],
    ["3 -(-1)", 4],
    ["2 + -2", 0],
    ["10- 2- -5", 13],
    ["(((10)))", 10],
    ["3 * 5", 15],
    ["-7 * -(6 / 3)", 14]
]

for test in tests:
    print(calc(test[0]))

while True:
    x = input("\n> ")
    print(calc(str(x)))