asyncssh compatible file-like object for capturing the most recent lines

last_lines.py

class Last_Lines:
  def __init__(self, n, binary=True):
    self.n = n
    self.binary = binary
    self.lines = []
    # asyncssh calls fstat() on fileno() and checks if it is a regular file
    # thus we open any regular file to fake it ...
    self.dev_null = open('/etc/resolv.conf')
  def write(self, s):
    lines = s.splitlines(True)
    self.writelines(lines)
    return len(s)
  def writelines(self, lines):
    if lines and self.lines and not self.lines[-1].endswith(b'\n' if self.binary else '\n'):
      self.lines[-1] += lines[0]
      lines.pop(0)
    for line in lines:
      self.lines.append(line)
    if len(self.lines) > self.n:
      for i in range(0, len(self.lines) - self.n):
        self.lines.pop(0)
  def fileno(self):
    return self.dev_null.fileno()
  def close(self):
    pass
  def getvalue(self):
    if self.binary:
      return b''.join(self.lines)
    else:
      return ''.join(self.lines)