This post is part 2 of the "Building a Blog" series:

Before anyting, the core task is generating blog posts with your prefered input format, like markdown, reST, AsciiDoc, etc. Personally I prefer wrting using markdown format. Because python is my major programming language, I write reST too, mainly to write documenation using sphinx. Also, I need the generating tool to be customizable, so I can extend it some specific needs, like generating special post etc.

## Pelican

At first I considered sphinx, as I'm already familiar with it, used it quite often, and supports math and many output format like latex. But the problem is also obvious: it's built for writing documenations and I find no good looking templage. And I realized that I do not really need latex output for a blog.

Then it comes to hexo, withing many suprisingly good templates. The downside is it's written in node.js, which I'm not familiar nor interested. I do not like the engine language, but the home page and templates are elegant. So I gave it a try.
I spent a day to write two plugins, one for marking specific content as confidential, another for filtering posts on some criteria. It turns out that wrting plugins for it is not pleasant, especially I'm not a fan of the language. Considering the possibility that I need to extent it futher, I think it's probably not a good choice.

Finally I choosed pelican as the static page generator. pelican is a popular python package for generating static pages, supporting markdown, reST, AsciiDoc out of the box, and is flexible to add new readers and generators etc. to extend it. It's using a language that I'm familiar with, it's easy to exent, but the downside is obviouse too: the home page looks, well, not beautiful at least. pelican uses python-markdown to parse markdown files, it is still actively developped, extensible, but the documenation is a nightmare. It's literally difficult to read, and even more difficult to find he information I want. At last I have to read the soursource code. Also I did not find an attractive template from the gallary.

But luckily, I found a beautiful template maupassant from hexo templates gallary that have been kindly ported to pelican by Rongqing Ye. It's originally developped by cho for Typecho.

## pelican Extionsions

I have some kind of specific requirement of generating posts:

1. mark a post as confidential content
2. filter posts by some criteria so I can generate a sub-blog
3. write reveal.js slides.

Like hexo, pelican's plugins is implemented with signals. Simply put, the generating process is splited to many steps, at each step pelican will emit specific signals, so you can register your function to do some processing. For example, there's a signals when pelican initialize, so you can get the configurations; there's a signal when readers are initialized, when you can register your reader for special input files. For details please find the documentations on how to create plugins

### Mark Confidential Post

I wrote a special function registered to article_generator_context, to collect confidential centents marked by a frontmatter metadata confidential. based on the value, this function may cleanup the summary to hide any information except the title from the index page, or change the status to draft, so the post will not be listed on any index page, or completely ignore the post, by setting the status to an invalid value that is not understood by pelican. But I will receive an error message about this. Before exit, I write the urls of all confidential posts, for later layer use.

### Filter Posts

The filter is similarly implemented: register a function that changes the status to some invalid value if it should not be included. So by specifying some topics in the frontmatter, I can generate a sub-blog that only contains post on the topic. This is helpful if I want a sub blog for relatively formal situations.

### Write reveal.js Slides

reveal.js is a framework for easily creating beautiful presentations using HTML. It'll be cool and handy to host slides too.

There's a fairly simple way to do so: just define a new template page, and specify it in the frontmatter. But things becomes a litte complicated when it comes to reveal.js: it uses <section> tag to indicate slides, but there's not such a thing in markdown. If this is not really a problem, as you can extend the parser, you have to be careful when you write html tags inside markdown, in case some markdown rules applied to html content, especially when you loaded many extensions.

To make things clear, I finally decided not to use markdown parsers in pelican, instead, use reveal.js markdown support, or write raw htmls directly. To do so, I added a new reader for special extensions .mds and .htmls. The frontmatter is processed just like a normal markdown file, but the content is not parsed. They are inserted directly to the corresponding predefined templates.

After a while, I wanted to add something else. Note that in the reveal.js official demo you canchange the style by clicking links. I'd like to support this too. After some expirements, I used a special mark to indicated a special slide being inserted. All I need is do some string find and replace after reading a file.

But when it comes to pdf export, things became complicated. While I can insert a setting slide now, practically it does not belong to the content and I did not want to include it when exporting to pdf files. Generating two versions? Not ideal. I need some html way solution.

First I marked these settings slide sections to a special no-print class, then use css to hide it when print:

@media print
{
.no-print, .no-print *
{
display: none !important;
}
}



Then I found that the content were hidden but left blank pages. As already I have marked these slides, I can directly remove these slides with javascript, connected to reveal.js ready event. Now these settings slides will not be exported!