next_url:   install.html
next_title: Installation
prev_title: Table of Contents
prev_url:   siteindex.html

Python-Markdown
===============

This is a Python implementation of John Gruber's 
[Markdown](http://daringfireball.net/projects/markdown/). 
It is almost completely compliant with the reference implementation,
though there are a few very minor [differences](#differences). See John's 
[Syntax Documentation](http://daringfireball.net/projects/markdown/syntax) 
for the syntax rules.

See the [installation instructions](install.html) to get started.

Goals
-----

The Python-Markdown project is developed with the following goals in mind:

* Maintain a Python 2 *and* Python 3 library (with an optional CLI wrapper)
  suited to use in web server environments (never raise an exception, never 
  write to stdout, etc.) as an implementation of the markdown parser that 
  follows the [syntax rules](http://daringfireball.net/projects/markdown/syntax)
  and the behavior of the original (markdown.pl) implementation as reasonably
  as possible (see [differences](#differences) for a few exceptions).

* Provide an [Extension API](extensions/api.html) which makes it possible
  to change and/or extend the behavior of the parser.

Features
--------

In addition to the basic markdown syntax, Python-Markdown supports the following
features:

* __International Input__

    Python-Markdown will accept [input](reference.html#text) in any language 
    supported by Unicode including bi-directional text. In fact the test suite 
    includes documents written in Russian and Arabic.

* __Extensions__

    Various [extensions](extensions/index.html) are provided (including 
    [extra](extensions/extra.html)) to change and/or extend the base syntax. 
    Additionally, a public [Extension API](extensions/api.html) is available 
    to write your own extensions.

* __Output Formats__

    Python-Markdown can output documents in HTML4, XHTML and HTML5. See the
    [Library Reference](reference.html#output_format) for details.

* __Command Line Interface__

    In addition to being a Python Library, a 
    [command line script](cli.html) is available for your convenience.

Differences
-----------

While Python-Markdown strives to fully implement markdown as described in the 
[syntax rules](http://daringfireball.net/projects/markdown/syntax), the rules 
can be interpreted in different ways and different implementations 
occasionally vary in their behavior (see the 
[Babelmark FAQ](http://johnmacfarlane.net/babelmark2/faq.html#what-are-some-examples-of-interesting-divergences-between-implementations)
for some examples). Known and intentional differences found in Python-Markdown 
are summarized below:

* __Middle-Word Emphasis__

    Python-Markdown defaults to ignoring middle-word emphasis. In other words,
    `some_long_filename.txt` will not become `some<em>long</em>filename.txt`.
    This can be switched off if desired. See the 
    [Library Reference](reference.html#smart_emphasis) for details.

* __Indentation/Tab Length__

    The [syntax rules](http://daringfireball.net/projects/markdown/syntax#list) 
    clearly state that when a list item consists of multiple paragraphs, "each 
    subsequent paragraph in a list item **must** be indented by either 4 spaces 
    or one tab" (emphasis added). However, many implementations do not enforce 
    this rule and allow less than 4 spaces of indentation. The implementers of 
    Python-Markdown consider it a bug to not enforce this rule. 

    This applies to any block level elements nested in a list, including
    paragraphs, sub-lists, blockquotes, code blocks, etc. They **must** always 
    be indented by at least four spaces (or one tab) for each level of nesting.

    In the event that one would prefer different behavior,
    [tab_length](reference.html#tab_length) can be set to whatever length is 
    desired. Be warned however, as this will affect indentation for all aspects 
    of the syntax (including root level code blocks).

* __Consecutive Lists__

    While the syntax rules are not clear on this, many implementations (including 
    the original) do not end one list and start a second list when the list marker
    (asterisks, pluses, hyphens, and numbers) changes. For consistency, 
    Python-Markdown maintains the same behavior with no plans to change in the 
    foreseeable future. That said, the [Sane List Extension](extensions/sane_lists.html)
    is available to provide a less surprising behavior.
    

Support
-------

You may ask for help and discuss various other issues on the [mailing list][] 
and report bugs on the [bug tracker][].

[mailing list]: http://lists.sourceforge.net/lists/listinfo/python-markdown-discuss
[bug tracker]: http://github.com/Python-Markdown/markdown/issues