Implement a simple calculator with Python

Calculator Development Requirements

1. Implementation of subtraction and extension priority resolution
2. User Input 1-2 * ((60-30 + ( -40/5) * (9-2*5/3 + 7/3*99/4*2998 +10 * 568/14))-( -4*3)/(16-3*2)) and other similar formulas, you must parse the inside (), +,-, *,/character Numbers and formulas, and the results must be consistent with the results of the actual calculator.

#coding =utf-8import redef Sub_calc (Formula): "" Calculates the value of a subtraction expression "" "flag = True while flag:m = Re.search (' \ \ D+\.? \d*[*/]-?\d+\.? \d* ', formula) #先匹配乘除 Example: 5.12 * -123.12,-5.12/ -123.12 If m:sub_mul_div = M.group () re            s = CALC_MULTI_DIVD (sub_mul_div) formula = Formula.replace (sub_mul_div,res) # Replaces the result of the multiplication expression, loops to determine if there is a multiplication expression  Print "*" * 10, "multiplication expression:", Formula Else:print "*" * 10, "multiplication calculated" flag = False print "*" * 10, "the expression after calculating multiplication in parentheses", formula result = Calc_add_stract (Formula) #计算加减法 return result def CALC_MULTI_DIVD (formula) : "" "computes a single multiplication expression" "" Print "*" * 20, "single multiplication expression", formula F_list = Re.split (' [*/] ', formula) print "*" * 20, "single multiply  In addition to the expression list ", f_list if ' * ' in formula:res = float (f_list[0]) * FLOAT (f_list[1]) elif '/' in formula:res =  Float (f_list[0])/float (f_list[1]) return str (RES) def calc_add_stract (Formula): "" Calculates the addition and subtraction, computes "" "by reduce 22" "" Print "*" * 20, "no sign of subtraction expression:", formula #对符号进行处理 formula = Formula.replace ('---', ' + ') formula = Formula.replace (' + + ')    Formula = Formula.replace ('-+ ', '-') formula = Formula.replace (' +-', '-') print "*" * 20, "add minus expression with sign:", formula #对一个加减表达式,-Becomes +-, in order to make a split list for the reduce calculation formula = Formula.replace ('-', ' +-') Formula_list = formula.split (' + ') pr int "*" * 20, "list divided by plus sign:", Formula_list #第一个数为负数, the first field in the list is empty if formula_list[0] = = ": Formula_list = Formula_lis            T[1:] "" result = 0 for i in formula_list:if '-' in i:stract_list = I.split ('-') result = Float (stract_list[0])-float (stract_list[1]) + result Else:result + = float (i) "" "Res  Ult = reduce (lambda x,y:float (x) + float (y), formula_list) print "*" * 20, "Add minus expression results:", result return Str (result) def  Calc (Formula): Flag = True while flag:m = Re.search (' \ ([^ ()]*\) ', formula) if M:print "*" * 5, "calculate the match to the bracket expression:", M.GRoup () Sub_formula = M.group (). Strip (' () ') res = Sub_calc (Sub_formula) #先计算括号内的表达式 F Ormula = Formula.replace (M.group (), res) #将表达式计算出来的结果替换原括号, once again cycle to determine if there are parentheses Else:flag = False print "* "* 5," The final post-brace expression: ", formula result = Sub_calc (Formula) return result if __name__ = = ' __main__ ': formula = "1-2 * ((60-30 + ( -9-2-5-2*3-5/3-40*4/2-3/5+6*3) * ( -9-2-5-2*5/3 + 7/3*99/4*2998 +10 * 568/14))-( -4*3)/(16-3*2)) "Print" Expression to evaluate: ", formula #去掉所有的空格 formula = re.sub (' \s ',", formula) print "expression after whitespace removed", Formula res = cal C (Formula) print "final result:", res

Implement a simple calculator with Python