Question

I’m new to Python, Google AppEngine and Jinja. If I’ve posted too much code below, I am sorry. This is my first posted question to StackOverflow.

I’m building a blog (for a class) and I need to replace newline characters “\n” in the user’s post. The function that queries the database sends it’s results to a render() function.

All the code works perfectly until I add the line of code that is supposed to replace the “\n.”

I’ve done a variety of edits and I just can’t deduce what the AppEngine, or Jinja, or Python wants me to do to satisfy it.

My database class sets up the db_blog Kind with four types, including ‘post_content‘

class db_blog(db.Model):
    post_subject = db.StringProperty(required = True)
    post_content = db.TextProperty(required = True)
    post_created = db.DateTimeProperty(auto_now_add = True)
    post_last_modified = db.DateTimeProperty(auto_now_add = True)

The ‘Newpost’ class I want this to receive the ‘query_select‘ object from the Blog class below.

class Newpost(webapp2.RequestHandler):
    def write(self, *args, **kwds):
        self.response.out.write(*args, **kwds)

    def render_str(self, template, **params):
        t = jinja_env.get_template(template)
        return t.render(params)

    def render(self, template, **kwds):
        self._render_text = self.post_content.replace("\n", "<br />") ##<-- See here 
        self.write(self.render_str(template, **kwds))

The Blog class gets all user posts and sends them to ‘Newpost’ to be rendered.

class Blog(Newpost):
    def get(self):
        query_select = db.GqlQuery("SELECT * FROM db_blog ORDER BY post_created DESC")
        self.render('blog_posts.htm', query_select = query_select)

1. As shown above, the code will generate this error:

AttributeError: ‘Blog’ object has no attribute ‘post_content’

I take it that class Blog needs to inherit from db_blog, so (See #2)

2. If I add db_blog to the Blog class’ parameter list I get a new error:

AttributeError: ‘NoneType’ object has no attribute ‘replace’

I think the error is telling me that I’m passing an object that doesn’t exist, so I’m really confused. If I comment-out the line trying to replace the “\n”character, this code runs perfectly – so how can it NOT be passing the object? Or claim it’s == None?

More importantly, how can I get it to work!

Much thanks to you who read this far, and kingdoms of wealth to s/he that can get me going.

Answer 1

The reason you are getting the attribute error is because the self in Newpost.get refers to the RequestHandler (Blog) and not to the post that you want. I suggest that, instead of defining the conversion in your view function, added it as a property on the model, e.g.

class db_blog(db.Model):

    post_subject = db.StringProperty(required = True)
    post_content = db.TextProperty(required = True)
    post_created = db.DateTimeProperty(auto_now_add = True)
    post_last_modified = db.DateTimeProperty(auto_now_add = True)

    @property
    def escaped_content(self):
        # possibly want to escape HTML in your post_content first
        return self.post_content.replace("\n", "<br />")

Then, you can just pass along query_select to your template (as you are currently doing now):

{% for post in query_select %}
{{ post.escaped_content | safe }}
{% endfor %}

You need to use safe above, because otherwise jinja will escape your <br />. Since I can’t see you template, I don’t know if this exactly fits what you are doing, but hopefully you get the point.

To explain the three lines of jinja above:

1. {% for post in query_select %} – just like a for loop, iterates over the posts, and each post should be a db_blog instance (from your query).
2. post.escaped_content is exactly equivalent to calling the escaped_content attribute of your db_blog model in Python.
3. {{ post.escaped_content | safe }} applies the safe filter to the string produced by escaped content (without safe, jinja would convert <br /> to <br /> (which would literally display <br /> on the page).
4. {% endfor %} ends the for loop.