# Kalculator

kalculator.py

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

from __future__ import print_function
import readline  # for better console text edit experience

def isnumeric(number):
    for num in range(10):
        if str(number[-1])==str(num):
            return True
    return False
try:
    input=raw_input
except:
    pass

def kalculator(string):
    '''
    this is the main function
    '''
    string = string.replace(' ', '')  # remove spaces. spaces will raise exceptions.
    string = string.replace('of', '/')  # O - of
    string = string.replace('**', '^')  # O - order by
    for num in range(10):
        string = string.replace(str(num) + '(', str(num) + '*(')
        string = string.replace(')' + str(num), ')*' + str(num))
    tokens = []
    for char in string:  # tokenize calculation
        if isnumeric(char):
            if len(tokens) > 0 and tokens[-1][-1]=='.':
                tokens[-1] += char
            elif len(tokens) > 0 and tokens[-1]=='-':
                tokens[-1] += char
            elif len(tokens) > 0 and isnumeric(tokens[-1]):
                tokens[-1] += char
            else:
                tokens.append(char)
        else:
            if char=='.':
                tokens[-1] += char
            else:
                tokens.append(char)
    while find(tokens, '('):  # find brackets B - brackets
        start = None
        end = None
        middle = []
        i = 0
        for token in tokens:  # calculate brackets
            if token == '(':
                start = i
                middle = []
            elif token == ')' and end == None:
                end = i
                tokens = tokens[:start] + calculator(middle) \
                    + tokens[end + 1:]
                break
            else:
                middle.append(token)
            i += 1
    result = calculator(tokens)[0]  # last calculation
    if result.endswith('.0'):
        result=result[:-2]
    return result


def calculator(tokens):
    '''
    calculate brackets less calculations
    '''

    while find(tokens, '^'):  # O - order by
        i = 0
        for token in tokens:
            if token == '^':
                tokens[i] = str(float(tokens[i - 1]) ** float(tokens[i
                                + 1]))
                tokens = tokens[:i - 1] + [tokens[i]] + tokens[i + 2:]
                break
            i += 1
    while find(tokens, '*') or find(tokens, '/'):
        i = 0
        for token in tokens:
            if token == '*':  # M - multiplication
                tokens[i] = str(float(tokens[i - 1]) * float(tokens[i
                                + 1]))
                tokens = tokens[:i - 1] + [tokens[i]] + tokens[i + 2:]
                break
            elif token == '/':

                             # D - Division

                tokens[i] = str(float(tokens[i - 1]) / float(tokens[i
                                + 1]))
                tokens = tokens[:i - 1] + [tokens[i]] + tokens[i + 2:]
                break
            i += 1
    while find(tokens, '+') or find(tokens, '-'):
        i = 0
        for token in tokens:
            if token == '+':  # A - Addition
                tokens[i] = str(float(tokens[i - 1]) + float(tokens[i
                                + 1]))
                tokens = tokens[:i - 1] + [tokens[i]] + tokens[i + 2:]
                break
            elif token == '-':

                             # S - Subtraction

                tokens[i] = str(float(tokens[i - 1]) - float(tokens[i
                                + 1]))
                tokens = tokens[:i - 1] + [tokens[i]] + tokens[i + 2:]
                break
            i += 1
    return tokens


def find(l, m):

    # list find function

    for item in l:
        if item == m:
            return True
    return False


if __name__ == '__main__':
    while True:
        i = input('>')
        try:
            print(kalculator(str(i)))
        except Exception as e:
            print('Error : ',str(e).replace('float','number'))

Kalculator

Use BODMAS method

1. B - brackets ()
2. O - of / order by ** ^
3. D - division /
4. M - multiplication *
5. A - addition +
6. S - subtraction -

this is a good example for developers.
i thinked hard.
at last I developed my own methods.
you can use python built-in calculator eg-:eval(input('>'))
but i made my own method.
this is a foundation for a interpreter.
thinking is the important thing.

Bye!

minus and point supported