用python求圆周率

from math import fabs          
from time import perf_counter  
def Bar(i):        
   N = pow(10,level)
   a = int((i/N)*50)
  b = 50 - a
Y , N = '*' * a , '.' * b
print("\r计算中：{:3.0f}% [{}->{}] {:.2f}s"
         .format(2*a,Y,N,perf_counter()),end='')
level = eval(input('计算Pi精确到小数点后几位数：'))
print('\n{:=^70}'.format('计算开始'))
a,b,pi,tmp = 1,1,0,1
i = 0
'''
a 分子  |  b 分母  |  pi 圆周率
tmp 存储a/b的值    |  i  执行进度
'''
perf_counter()      
while (fabs(tmp) >= pow(10,-level)):
   pi += tmp
   b += 2
   a = -a
   tmp = a/b
   i += 2
   Bar(i)        
print('\n{:=^70}'.format('计算完成'))
print('\nPi的计算值为：{}'.format(round(pi*4,level))