Python3 string calculator

calc.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

from calc_parser import calc_parser


def evaluate(expression: list):
    for i in range(len(expression)):
      if expression[i] != '+' and expression[i] != '-' and expression[i] != '*' and expression[i] != '/':
        if '.' in expression[i]:
          expression[i] = float(expression[i])
        else:
          expression[i] = int(expression[i])
    while '/' in expression or '*' in expression:
      for i, _ in enumerate(expression):
          if expression[i] == '/':
              expression[i] = expression[i-1] / expression[i+1]
              del expression[i+1]
              del expression[i-1]
          elif expression[i] == '*':
              expression[i] = expression[i-1] * expression[i+1]
              del expression[i+1]
              del expression[i-1]
    while '-' in expression:
      for i, _ in enumerate(expression):
        if expression[i] == '-':
              expression[i] = expression[i-1] - expression[i+1]
              del expression[i+1]
              del expression[i-1]
    while '+' in expression:
      for i, _ in enumerate(expression):
          if expression[i] == '+':
              expression[i] = expression[i-1] + expression[i+1]
              del expression[i+1]
              del expression[i-1]
    return expression[0]

# examples:
# «8 * 5.003 / 5.34 + 8 - 3.4» > 12.095131086142322
# «65 *     90 -   56 /  9.0» > 5843.777777777777
# «562/832     *   732+ 32» > 526.4519230769231
# «324*32+87» > 10455
  
string = input()
expression = calc_parser(string)
print(evaluate(expression))

calc_parser.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

def calc_parser(string: str):
    digits = [
        '1', '2', '3', '4', '5', '6', '7', '8', '9', '0'
    ]
    dot = '.'

    def _isint(string: str):
        for char in string:
            if not (char in digits):
                return False
        return True

    def _isfloat(string: str):
        for char in string:
            if not (char in digits):
                if not (char is dot):
                    return False
        if dot in string:
            return True
        else:
            return False

    rslt = []
    i = 0
    while len(string) > 1 and ('+' in string or '-' in string or '/' in string or '*' in string):
        if string[i] == '+' or string[i] == '-' or string[i] == '/' or string[i] == '*':
            if _isint(string[:i]) or _isfloat(string[:i]):
                rslt.append(string[:i])
                rslt.append(string[i])
                if len(string) > 1:
                    string = string[i + 1:]
                else:
                    string = ''
            else:
                return []
            i = 0
        elif string[i] == ' ':
            string = '%s%s' % (string[:i], string[i + 1:])
        else:
            i += 1
    rslt.append(string)
    return rslt