Read N Characters Given Read4

class Solution:
    def read(self,buf,n):
        buffer = [0]*4
        readi = pos = 0
        while True:
            size = read4(buffer)
            readi = 0
            while readi < size and pos < n:
                buf [pos] = buffer[readi]
                readi += 1
                pos+=1
            if size == 0 or pos == n:
                return pos