Adding comments

Write the comment flow with add_comment.

Link comments to a Post

In the first lesson we defined the Comment class but didn't link it to posts. Now we add a field comments: list = field(default_factory=list) to the Post class. Every post then has its own comment list.

Next we write the add_comment method inside Post: self.comments.append(comment). To add a comment you call p.add_comment(Comment(author="Ali", text="Nice")). len(p.comments) gives the comment count.

Where the method lives matters

You write add_comment inside the Post class because a comment belongs to a post. Putting it on Blog would be wrong; a blog holds many posts and wouldn't know which post to add the comment to.

The method body calls self.comments.append(comment). Here self is the current post instance and comments is its own list. This separation keeps each post's comments apart.

Exercise Add comments to the Post class

Add a field comments: list = field(default_factory=list) to the Post class above and write def add_comment(self, comment): with the body self.comments.append(comment). Then create p = Post(title="First", author="Ayşe"), add two comments and print the count with print(len(p.comments)).

Show example solution

from dataclasses import dataclass, field

@dataclass
class Post:
    title: str = ""
    content: str = ""
    author: str = ""
    comments: list = field(default_factory=list)

    def add_comment(self, comment):
        self.comments.append(comment)

@dataclass
class Comment:
    author: str = ""
    text: str = ""

@dataclass
class Blog:
    posts: list = field(default_factory=list)

    def add_post(self, post):
        self.posts.append(post)

p = Post(title="First", author="Ayşe")
p.add_comment(Comment(author="Ali", text="Nice one"))
p.add_comment(Comment(author="Veli", text="Thanks"))
print(len(p.comments))

Test yourself

Match the comment-adding concepts

comments

A post's comment list
add_comment

Comment-adding method
append

Add to the end
len

Count function
Which class should add_comment belong to?
- The Blog class
- The Comment class
- The Post class
- Left at module level
Show answer

The Post class — A comment is tied to a post, so add_comment lives on the Post class.

Parameter of add_comment

    def add_comment(self, ____):
        self.comments.append(comment)

Show answer

    def add_comment(self, comment):
        self.comments.append(comment)

Next lesson: Search and filter

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