This is a Python implementation of John Gruber's Markdown. It is almost completely compliant with the reference implementation, though there are a few very minor differences. See John's Syntax Documentation for the syntax rules.
The Python-Markdown project is developed with the following goals in mind:
Maintain a Python 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 and the behavior of the original (markdown.pl) implementation as reasonably as possible (see differences for a few exceptions).
Provide an Extension API which makes it possible to change and/or extend the behavior of the parser.
In addition to the basic markdown syntax, Python-Markdown supports the following features:
Python-Markdown will accept input in any language supported by Unicode including bi-directional text. In fact the test suite includes documents written in Russian and Arabic.
Python-Markdown can output documents with either HTML or XHTML style tags. See the Library Reference for details.
Command Line Interface
In addition to being a Python Library, a command line script is available for your convenience.
While Python-Markdown strives to fully implement markdown as described in the syntax rules, the rules can be interpreted in different ways and different implementations occasionally vary in their behavior (see the Babelmark FAQ for some examples). Known and intentional differences found in Python-Markdown are summarized below:
Python-Markdown defaults to ignoring middle-word emphasis (and strong emphasis). In other words,
some_long_filename.txtwill not become
some<em>long</em>filename.txt. This can be switched off if desired. See the Legacy EM Extension for details.
The syntax rules 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 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). Alternatively, a third party extension may offer a solution that meets your needs.
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 is available to provide a less surprising behavior.
You may report bugs, ask for help, and discuss various other issues on the bug tracker.