thread.py

from exceptions import PermissionDenied
"""
Thread:

A Thread is created with a title, and a first post.
The owner of the thread is the author of the first post.
Any user can add a new post to the thread.
A user can only remove their own post from the thread.
The thread owner can edit the title and the tags, but other users cannot.
"""

class Thread:
  def __init__(self, title, first_post):  #First post is an object.
    """
    Creates a new thread with a title and an initial first post.
    The author of the first post is also the owner of the thread.
    The owner cannot change once the thread is created.
    """
    self.owner = first_post.author
    self.tags = []
    self.title = title
    self.posts = [first_post]

  def get_owner(self):
    """
    Returns the owner of the thread.
    """
    return self.owner

  def get_title(self):
    """
    Returns the title of the thread.
    """
    return self.title

  def get_tags(self):
    """
    Returns a sorted list of unique tags.
    """
    return sorted(self.tags)

  def get_posts(self):
    """
    Returns a list of posts in this thread, in the order they were published.
    """
    return self.posts

  def publish_post(self, post):
    """
    Adds the given post object into the list of posts.
    """
    self.posts.append(post)

  def remove_post(self, post, by_user):
    """
    Allows the given user to remove the post from this thread.
    Does nothing if the post is not in this thread.
    * raises PermissionDenied if the given user is not the author of the post.
    """

    if post in self.posts:
        if by_user == post.author:
            location = self.posts.index(post)
            del self.posts[location]
        else:
            raise PermissionDenied

  def set_title(self, title, by_user):
    """
    Allows the given user to edit the thread title.
    * raises PermissionDenied if the given user is not the owner of the thread.
    """
    if by_user == self.posts[0].author:
        self.title = title
    else:
        raise PermissionDenied

  def set_tags(self, tag_list, by_user):
    """
    Allows the given user to replace the thread tags (list of strings).
    * raises PermissionDenied if the given user is not the owner of the thread.
    """
    if by_user == self.owner:
        seen = []
        for x in tag_list:
            if x not in seen:
                seen.append(x)
        self.tags = seen
    else:
        raise PermissionDenied