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Eric Holscher Django Under The Hood November 6, 2015 Understanding Documentation Systems

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Who am I • Co-Founder of Read the Docs • Co-Founder of Write the Docs

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Today • Learn about Docutils/RST internals • Learn how Sphinx builds on top & extends RST • Understand how Django uses these tools, and how you can too

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Documentation Systems

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Sphinx • Extends RST with additions for documenting so ware • Has powerful semantic constructs

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Semantic Meaning • The power of HTML, and RST • What something is, not what it looks like • Once you know what it is, you can display it properly • Separation of Concerns

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# HTML (Bad) issue 72 # HTML (Good) issue 72 # CSS .issue { text-format: bold; } Classic HTML Example

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# Bad Warning: Don’t do this! # Good Don’t do this! # Best .. warning:: Don’t do this Classic RST Example

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# Markdown Check out [PEP 8](https:// www.python.org/dev/peps/pep-0008/) # RST Check out :pep:`8` Markdown vs. RST

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Semantic Markup shows the intent of your words

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+----------------------------------------------------------+ | | | Read the Docs | | +----------------------------------------------+ | | | | | | | Sphinx | | | | +-----------------------------------+ | | | | | | | | | | | Docutils | | | | | | +--------------------+ | | | | | | | | | | | | | | | reStructuredText | | | | | | | | | | | | | | | +--------------------+ | | | | | | | | | | | | | | | | | | | | | | | +-----------------------------------+ | | | | | | | | | | | | | | | +----------------------------------------------+ | | | | | +----------------------------------------------------------+ Tech Overview

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Docutils

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Parts • Reader • Parser • Transformer • Writer

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How it fits together

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Reader • Get input and read it into memory • Quite simple, generally don’t need to do much

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Title ===== Paragraph. Words that have **bold in them**. Reader Example

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[u'Title', u'=====', u'', u'Paragraph.', u'', u'Words that have **bold in them**.'] Reader Example

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Reader’s are useful for adding non-ﬁlesystem types of input (StringIO, Network)

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Parser • Takes the input and actually turns it into a Doctree • RST is the only parser implemented in Docutils • Handles directives, inline markup, etc. • Implemented with a lined-based recursive state machine

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Doctree • AST for Docutils • Source of Truth • Tree structure with a document at the root node • Made up of a series of Nodes

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[u'Title', u'=====', u'', u'Paragraph.', u'', u'Words that have **bold in them**.'] Parser Example

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Title Paragraph. Words that have bold in them Parser Example

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Nodes • Structural Elements •document, section, sidebar • Body Elements • paragraph, image, note • Inline Elements •emphasis, strong, subscript

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Nodes • Most common types of nodes are Text Nodes •nodes.paragraph(rawsource, nodes_or_text)

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RST Directives • Allow block level extension of RST •.. note:: Foo = [ Node]

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RST Interpreted Text Roles • Allows paragraph level extension of RST •:pep:`8` = [ Node]

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RST Parser • Really neat language • Some directives are tied to RST because of internal, recursive parsing

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.. note:: Wootles *blog* Wootles blog RST Parser

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RST Parser • Recursively parses RST inside nodes • Python objects not portable • Need to think about how to port this to other parsers in the future

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RST lets you create arbitrary markup that matches the semantics of your problem space

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Parsers are used for implementing new RST features or adding new markup languages

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Transformer • Take the doctree and modify it in place • Allows for “full knowledge” of the content • Table of Contents • Generally implemented by traversing nodes of a certain type

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Title Paragraph. Words that have bold in them Transform Example

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Title Words that have bold in them Paragraph. Transform Example

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Transformers are used for changing the document in a way that requires full knowledge

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Writer • Takes the Doctree and writes it to actual ﬁles • HTML, XML, PDF, etc. • Translator does most of the work • Implemented with the Visitor pattern

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Visitor • Allows you to have arbitrary types of node’s and build `visit_` methods a er the fact • Generally a Directive creates an arbitrary Node type, which is converted by the Translator

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class MyHTMLVisitor(nodes.GenericNodeVisitor): def visit_foo(self, node): self.body.append(‘

’) def depart_foo(self, node): self.body.append('

\n') Translator

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Title Words that have bold in them Paragraph. Writer Example

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Title

Words that have bold in them.

Paragraph.

Writer Example

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Writers are used to change or add new output formats from the Doctree

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How it fits together

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Implementation

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# docutils/core.py self.document = self.reader.read(self.source, self.parser, self.settings) self.apply_transforms() self.writer.write(self.document, self.destination) Publisher

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# docutils/core.py self.document = self.reader.read(self.source, self.parser, self.settings) self.apply_transforms() self.writer.write(self.document, self.destination) Publisher

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# docutils/readers/__init__.py def read(self, source, parser, settings): self.source = source if not self.parser: self.parser = parser self.settings = settings self.input = self.source.read() document = self.new_document() self.parse(self.input, document) return document Reader

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# docutils/readers/__init__.py def parse(self, inputstring, document): """Parse `inputstring` and populate `document`, a document tree.""" self.statemachine = states.RSTStateMachine( state_classes=self.state_classes, initial_state=self.initial_state) inputlines = docutils.statemachine.string2lines( inputstring) self.statemachine.run(inputlines, document) RST Parser

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# docutils/core.py self.document = self.reader.read(self.source, self.parser, self.settings) self.apply_transforms() self.writer.write(self.document, self.destination) Publisher

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# docutils/core.py def apply_transforms(self): self.document.transformer.populate_from_components( (self.source, self.reader, self.reader.parser, self.writer, self.destination)) self.document.transformer.apply_transforms() Transforms

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# docutils/transforms/__init__.py def apply_transforms(self): """Apply all of the stored transforms, in priority order.""" while self.transforms: priority, transform_class, pending, kwargs = self.transforms.pop() transform = transform_class(self.document, startnode=pending) transform.apply(**kwargs) Transforms

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# docutils/core.py self.document = self.reader.read(self.source, self.parser, self.settings) self.apply_transforms() self.writer.write(self.document, self.destination) Publisher

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Writer # docutils/writers/__init__.py def write(self, document, destination): self.translate() output = self.destination.write(self.output) return output

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Writer # docutils/writers/__init__.py def write(self, document, destination): self.translate() output = self.destination.write(self.output) return output

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# docutils/writers/html4css1/__init__.py def translate(self): visitor = self.translator_class(self.document) self.document.walkabout(visitor) self.output = self.apply_template() Translator

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# docutils/core.py self.document = self.reader.read(self.source, self.parser, self.settings) self.apply_transforms() self.writer.write(self.document, self.destination) Publisher

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We now have an HTML (or whatever Writer) document on the disk

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Sphinx Implementation

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Sphinx • Builds on top of the standard docutils concepts • Add it’s own abstractions, but uses the same docutils machinery underneath

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Sphinx Architecture

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Major Sphinx Components • Application • Environment • Builder

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Sphinx Application • Main level of orchestration for Sphinx • Handles conﬁguration & building • Sphinx()

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Sphinx Environment • Keeps state for all the ﬁles for a project • Serialized to disk in between runs • Works as a cache

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Sphinx Builder • Wrapper around Docutils Writer’s • Generates all types of outputs • Generates most HTML output through Jinja templates instead of Translators

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Sphinx Architecture

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Typical Sphinx Run

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make html

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sphinx-build -b html -d _build/environment . _build/html

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# sphinx/application.py app = Sphinx(srcdir, confdir, outdir, doctreedir, opts.builder, confoverrides, status, warning, opts.freshenv, opts.warningiserror, opts.tags, opts.verbosity, opts.jobs) app.build(opts.force_all, filenames) Sphinx

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# sphinx/application.py def build(self, force_all=False, filenames=None): self.builder.compile_all_catalogs() self.builder.build_all() Sphinx Application

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# sphinx/application.py def build(self, force_all=False, filenames=None): self.builder.compile_all_catalogs() self.builder.build_all() Sphinx Application

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# sphinx/builders/__init__.py def build_all(self, docnames, summary=None, method='update'): # Read files from disk and put them in the env updated_docnames = set(self.env.update(self.config, self.srcdir, self.doctreedir, self.app)) # Write the actual output to disk self.write(docnames, list(updated_docnames), method) Sphinx Builder

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# sphinx/environment.py def update(self, config, srcdir, doctreedir, app): reader = SphinxStandaloneReader(parsers=self.config.source_parsers) pub = Publisher(reader=reader, writer=SphinxDummyWriter(), destination_class=NullOutput) source = SphinxFileInput(app, self, source=None, source_path=src_path, encoding=self.config.source_encoding) pub.publish() doctree = pub.document doctree_filename = self.doc2path(docname, self.doctreedir, '.doctree') dirname = path.dirname(doctree_filename) if not path.isdir(dirname): os.makedirs(dirname) f = open(doctree_filename, 'wb') pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL) Sphinx Environment

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# sphinx/builders/html.py def write(self, build_docnames, updated_docnames, method=‘update'): for docname in list(build_docnames + updated_docnames): self.docwriter.write(doctree, destination) self.docwriter.assemble_parts() body = self.docwriter.parts['fragment'] metatags = self.docwriter.clean_meta ctx = self.get_doc_context(docname, body, metatags) self.handle_page(docname, ctx, event_arg=doctree) Sphinx Builder

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# docutils/writers/__init__.py def write(self, document, destination): self.translate() output = self.destination.write(self.output) Docutils Writer

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# docutils/writers/__init__.py def write(self, document, destination): self.translate() output = self.destination.write(self.output) Docutils Writer

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# sphinx/writers/html.py def translate(self): visitor = self.builder.translator_class( self.builder, self.document) self.document.walkabout(visitor) self.output = visitor.astext() Sphinx Writer

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# sphinx/builders/html.py def handle_page(self, pagename, addctx, templatename='page.html'): ctx = self.globalcontext.copy() output = self.templates.render(templatename, ctx) f = codecs.open(outfilename, 'w', encoding, 'xmlcharrefreplace') f.write(output) Sphinx Builder

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We now have a fully templated HTML ﬁle on disk

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Sphinx Core Events allow you to hook into most parts of the build process

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Sphinx Core Events • builder-inited • source-read • doctree-read • doctree-resolved • env-updated • html-page-context • build-ﬁnished

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Sphinx Architecture

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Examples

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Markdown Parser • Uses recommonmark as a bridge • Translates Commonmark Node’s into Docutils Node’s

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## Markdown Header Hey There Markdown Parser

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Markdown Header Hey There Markdown Parser

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# recommonmark/parser.py def reference(block): # Commonmark Block ref_node = nodes.reference() # Docutils Node label = make_refname(block.label) ref_node['name'] = label ref_node['refuri'] = block.destination ref_node['title'] = block.title return ref_node Markdown Parser

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from recommonmark.parser import CommonMarkParser source_parsers = { '.md': CommonMarkParser, } source_suffix = ['.rst', '.md'] Enable Markdown

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:name[content]{key=val} :smallcaps[content] :ref[scatter plot]{target=myFigure} Proposed Markdown Inline Markup

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::: name [inline-content] {key=val} contents, can contain further block elements ::: :::eval [label] {.python} x = 1+1 print x ::: Proposed Markdown Block level Markup

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Table of Contents • Enabled with `.. contents::` Directive • Adds a pending node during parsing • Transform turns pending into a list of references

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.. contents:: TOC Getting Started ——————————————— Table of Contents

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TOC .. internal attributes: .transform: docutils.transforms.parts.Contents .details: Table of Contents

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TOC Getting Started Table of Contents

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References • Allow you to deﬁne and point at arbitrary points in documents • Sphinx makes them work across an entire project

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.. page 1 .. _my-title: Title ----- Paragraph .. page 2 Look at the :ref:`my-title`. References

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References

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References

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Intersphinx • Allows you to link across Sphinx projects, semantically •:ref:`django:template-loaders`

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intersphinx_mapping = { 'python': ('http://python.readthedocs.org/en/latest/', None), 'django17': ('http://django.readthedocs.org/en/1.7/', None), 'django18': (‘http://sphinx.readthedocs.org/en/1.8/', None), } Intersphinx

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Reference Resolution Order • References • Domains • Intersphinx References • Intersphinx Domains

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How Django uses Sphinx

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Django Deployment • All documentation is written in RST • HTML generated at JSON blobs • Rendered through Django templates on the website

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:ticket:`1325` :setting:`MEDIA_URL` Django specific additions

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.. snippet:: :filename: part1.py print “hello world” Django specific additions

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def ticket_role(name, rawtext, text, lineno, inliner): num = int(text.replace('#', '')) url_pattern = inliner.document.settings.env.app.config.ticket_url url = url_pattern % num node = nodes.reference(rawtext, '#' + utils.unescape(text), refuri=url) return [node], [] Ticket Role

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class snippet_with_filename(nodes.literal_block): pass Snippet Node

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class SnippetWithFilename(Directive): has_content = True optional_arguments = 1 option_spec = {'filename': directives.unchanged_required} def run(self): code = '\n'.join(self.content) literal = snippet_with_filename(code, code) if self.arguments: literal['language'] = self.arguments[0] literal['filename'] = self.options['filename'] set_source_info(self, literal) return [literal] Snippet Directive

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def visit_snippet(self, node): lang = self.highlightlang fname = node['filename'] highlighted = highlighter.highlight_block(node.rawsource) starttag = self.starttag(node, 'div', suffix='', CLASS='highlight-%s' % lang) self.body.append(starttag) self.body.append('

\n' % (fname,)) self.body.append(highlighted) self.body.append('\n') raise nodes.SkipNode Snippet visitor

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These are generally useful for Django users, and should probably be released as a third party app

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Take Aways

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Make sure to use semantic markup when writing docs

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Generally your job is to get the nodes to exist in the way that you want

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Feel empowered to extend RST & Sphinx, and make them your own

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Understand where you need to plug into the pipeline, and do as little as possible to make it happen

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Thanks • @ericholscher • [email protected] • Come talk to me around the sprints