A simple calculator (SCW TU/e March 2021)

README.md

Example usage:

$ python arith.py 1 + 1
2
$ python arith.py 3 x 4
12
$ python arith.py 5 + 4 x 3
17
$ python arith.py 4 / 2
2
$ python arith.py 4 / 3 + 6 x 3
19.333333333333332

arith.py

#!/usr/bin/env python3

import re
import sys


def divide_args(a, b):
  if b == 0:
    raise ZeroDivisionError('cannot divide by zero')
  r = a / b
  if isinstance(r, float) and r.is_integer():
    r = int(r)
  return r

def find_operator(args, ops='all'):
  if ops == 'all':
    index, op = find_operator(args, 'x/')
    if not index:
      index, op = find_operator(args, '+-')
    return (index, op)

  for i, arg in enumerate(args):
    if isinstance(arg, str) and arg in ops:
      return (i, arg)
  return (False, False)

def parse_arg(arg):
  if not isinstance(arg, str):
    return arg
  if re.fullmatch('\d+', arg):
    return int(arg)
  elif re.fullmatch('\d+.\d*', arg):
    return float(arg)
  raise 'invalid argument'


try:
  arguments = list(sys.argv)
  arguments.pop(0)
  while True:
    index, op = find_operator(arguments)
    if not index:
      break

    arguments.pop(index)
    arg1 = parse_arg(arguments.pop(index - 1))
    arg2 = parse_arg(arguments.pop(index - 1))
    result = {
      '+': lambda a, b: a + b,
      '-': lambda a, b: a - b,
      'x': lambda a, b: a * b,
      '/': divide_args
    }[op](arg1, arg2)
    arguments.insert(index - 1, result)

  if len(arguments) == 1:
    print(arguments[0])
  else:
    print('error')
    print(arguments)
except ZeroDivisionError as err:
  print(err)