import re#source为计算表达式字符串
source='((100-15*(10.2/2)))*10+(9+8/2*4)'#判断字符串中无效字符函数
def check(s):
flag=True
if re.findall('[a-zA-Z]',s):
print('Invalid')
flag=False
returnflag#将表达式字符串中的空格，++等字符进行修正
def format(s):
s=s.replace(' ','')
s=s.replace('++','+')
return s#加法和减法函数
def cal_add_sub(s):
while re.search('\d+\.?\d*[-+]\d+\.?\d*', s):
print(s)
ret = (re.search('\d+\.?\d*[-+]\d+\.?\d*', s)).group()
x, y = re.split('[-+]', ret)
x = float(x)
y = float(y)
if re.search('\+',ret):
ret1 = x + y
s = re.sub('\d+\.?\d*[-+]\d+\.?\d*', str(ret1), s, 1)
elif re.search('\-',ret):
ret1 = x - y
s = re.sub('\d+\.?\d*[-+/]\d+\.?\d*', str(ret1), s, 1)
else:
z=re.search('\d+\.?\d*',s).group()
return z
#乘法和除法函数
defcal_mul_div(s):
while re.search('\d+\.?\d*[*/]\d+\.?\d*',s):
print(s)
ret = (re.search('\d+\.?\d*[*/]\d+\.?\d*', s)).group()
x,y=re.split('[*/]',ret)
x=float(x)
y=float(y)
if re.search('\*',ret):
ret1=x*y
print(ret1)
s = re.sub('\d+\.?\d*[*/]\d+\.?\d*', str(ret1), s, 1)
elif re.search('/',ret):
ret1=x/y
print(ret1)
s = re.sub('\d+\.?\d*[*/]\d+\.?\d*', str(ret1), s, 1)
else:
z=cal_add_sub(s)
return z#计算过程if check(source):
strs=format(source)
while re.search('\(',strs):
ret=re.search('\([^()]+\)',strs).group()
ret=cal_mul_div(ret)
strs=re.sub('\([^()]+\)',cal_mul_div(ret),strs,1)
else:
strs=cal_mul_div(strs)
print(strs)【使用正则表达式实现（加减乘除）计算器(python实现)】
