Use 50 lines of Python code to create a calculator

Use 50 lines of Python code to create a calculator
In this article, I will show you how to parse and calculate a four-digit arithmetic expression just like a common calculator. When we end, we will get a calculator that can process expressions such as 1 + 2 *-(-3 + 2)/5.6 + 3. Of course, you can also expand it more powerful. No nonsense. directly add the Code:

#!/usr/bin/env python# -*- coding: utf-8 -*-#_auth by kk# calc.py - # A simple calculator without using evalimport operator as opfrom plyplus import Grammar, STransformercalc_grammar = Grammar("""    start: add;    ?add: (add add_symbol)? mul;    ?mul: (mul mul_symbol)? atom;    @atom: neg | number | '\(' add '\)';    neg: '-' atom;    number: '[\d.]+';    mul_symbol: '\*' | '/';    add_symbol: '\+' | '-';    WS: '[ \t]+' (%ignore);""")class Calc(STransformer):    def _bin_operator(self, exp):        arg1, operator_symbol, arg2 = exp.tail        operator_func = { '+': op.add, '-': op.sub, '*': op.mul, '/': op.div }[operator_symbol]        return operator_func(arg1, arg2)    number      = lambda self, exp: float(exp.tail[0])    neg         = lambda self, exp: -exp.tail[0]    __default__ = lambda self, exp: exp.tail[0]    add = _bin_operator    mul = _bin_operatordef main():    calc = Calc()    while True:        try:            s = raw_input('> ')        except EOFError:            break        if s == '':            break        tree = calc_grammar.parse(s)        print(calc.transform(tree))main()

 

Note: Since the plyplus module is available in the beginning, you may remember to use pip install plyplus for installation. The final effect is [root @ django opt] # python cacl. py> 1 + 2 *-(-3 + 2)/5.6 + 34.35714285714>