Python reads super large files based on read(size) method

def readlines(f, separator):
  '''
   Read large files
   :param f: file handle
   :param separator: The separator for each line
   :return:
   '''
  buf = ''
  while True:
    while separator in buf:
      position = (separator) # The position of the delimiter      yield buf[:position] # Slice, from the start position to the delimiter position      buf = buf[position + len(separator):] # Slice again, cut out the yield data, and retain the remaining data
    chunk = (4096) # Read 4096 data into buf at one time    if not chunk: # If no data is read      yield buf # Return data in buf      break # Finish    buf += chunk # If read has data, add the read data to buf

with open('',encoding='utf-8') as f:
  for line in readlines(f,'|||'):
    # Why can readlines function be traversed using for loop? Because this function has the yield keyword, it is a generator function...    print(line)