Python中质数怎么找？

import time

import math

start=time.process_time()

m=input('please enter  an integer:')

i = int(m)

#创建一个空list0                                                        

r=list()

#添加元素2

r.append(2)

#从3开始挨个筛选

for a in range(3,i):

b=False

#用a除以小于a的质数b

for b in r:

if a%b==0:

b=False

break

else:

b=True

if b==True:

r.append(a)

print(r)

t=(time.process_time()-start)

print(t)