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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def validate (self):
 """Returns True if this Sequence is valid, False otherwise. Validation error messages are stored in self.messages. """

    if not os.path.isfile(self.pathname):
      self.message.append('Filename "%s" does not exist.')
    else:
      try:
        with open(self.pathname, 'r') as stream:
          pass
      except IOError:
        self.messages.append('Could not open "%s" for reading.' % self.pathname)

    for line in self.commands:
      messages = [ ]
      if line.cmd and not line.cmd.validate(messages):
        msg = 'error: %s: %s' % (line.cmd.name, " ".join(messages))
        self.log.messages.append(msg)

    return len(self.log.messages) == 0