Find four digit numbers from a string and then print numbers which are primes

I have this code to find four digit numbers from a string:

import re
pattern = re.compile(r"[1-9]\d{3}")
numbers = '0922035963126927190699198371937793731321758941428'
four_digits = pattern.findall(numbers)

My output is:

['9220', '3596', '3126', '9271', '9069', '9198', '3719', '3779', '3731', '3217', '5894', '1428']

And then from output list I want to print only prime numbers. I tried using this code:

def prime_factor(four_digits):
prime = []
for i in four_digits:
    flag = 0
    if i==1:
        flag=1
    for j in range(2,i):
        if i%j == 0:
            flag = 1
            break
    if flag ==0:
        prime.append(i)            
return prime

But it returns as an error:

line 13, in prime_factor
for j in range(2,i):

TypeError: 'str' object cannot be interpreted as an integer

What am I doing wrong and is there a better way to do this task?

>Solution :

Replace:

four_digits = pattern.findall(numbers)

by:

four_digits = [int(p) for p in pattern.findall(numbers)]

to convert your list of strings to a list of int.