pymd4c 0.4.7.0b1

Python bindings for MD4C

PyMD4C

Python bindings for the very fast MD4C Markdown parsing and rendering library.

• GitHub: https://github.com/dominickpastore/pymd4c
• PyPI: https://pypi.org/project/pymd4c/
• Changelog: https://github.com/dominickpastore/pymd4c/blob/master/CHANGELOG.md
• Issues: https://github.com/dominickpastore/pymd4c/issues

Introduction

The MD4C C library provides a SAX-like parser that uses callbacks to return the various blocks, inlines, and text it parses from the Markdown input. In addition, it provides an HTML renderer that wraps the generic parser to provide HTML output directly.

Accordingly, this Python module provides two classes:

• md4c.GenericParser - Wraps the generic SAX-like MD4C parser. Requires Python functions (or other callables) as callbacks.
• md4c.HTMLRenderer - Wraps the HTML renderer. Produces HTML output directly.

If other renderers are added to MD4C, they will get their own Python class as well, similar to the HTMLRenderer.

Install from PyPI

PyMD4C is available on PyPI under the name pymd4c. Install it with pip like this:

pip install pymd4c

This is the recommended method to obtain PyMD4C. It should work well on most Linux distributions. It will probably work well on Windows and macOS (but these platforms are not as well-tested).

If this does not work, there are a couple potential reasons:

1. You do not have pip installed, or your version is too old. See Installing Packages - Python Packaging User Guide.

2. Your version of Python is too old. This is a platform wheel, so it is built for each Python version separately. Python versions older than 3.6 are not supported. If your Python version is older than that, try upgrading.

3. Your platform is incompatible. Again, since it is a platform wheel, it is built for each supported platform separately.

   • If you are running Windows, you may be running 32-bit (x86) Python. Currently, only packages for 64-bit (x86-64) Python are built. If you can, try running 64-bit Python.
   • If you are on macOS, your macOS version might be too old.
   • If you are on Linux, you may be running on an architecture other than x86-64, a distribution that is too old, or a more esoteric distribution unsupported by manylinux2014. (Note that many architectures supported by manylinux2014 are not built at this time, including x86, arm64, ppc64le, and s390x.)
   • If you are on some other platform, unfortunately, it is not supported by the pre-built packages.

If a build is not available for your platform (or you simply want to), you can build and install from source. The instructions below should assist.

If a build is not available or not working for your platform and you think it should be, consider opening a GitHub issue.

Build and Install from Source

Prerequisites

This package depends on the MD4C library. It may be available through your package manager. Otherwise, it can be built from source as follows:

1. Make sure you have CMake and a C compiler installed.
2. Download and extract the matching release from the MD4C releases page (e.g. for PyMD4C version W.X.Y.Z, download MD4C version W.X.Y).
3. On Unix-like systems (including macOS):

   • Inside the extracted file, run the following:

     mkdir build
     cd build
     cmake ..
     make
     # Do as root:
     make install
     

     The install step must be run as root. The library will install to /usr/local by default.

   • You may need to rebuild the ldconfig cache (also as root): ldconfig

4. On Windows:

   • Inside the extracted file, run the following:

     mkdir build
     cd build
     cmake -DCMAKE_BUILD_TYPE=Release ..
     cmake --build . --config Release
     cmake --install .
     

     The library will install to "C:/Program Files (x86)/MD4C/" by default.

In addition, on Unix-like systems (including macOS), the pkg-config tool must be available to build PyMD4C. After PyMD4C is built, it is no longer required (that is, it is not a prerequisite for actually using PyMD4C). This tool is likely available on your system already, so this should not be an issue in most cases.

Finally, note that since this package uses C extensions, development headers for Python must be installed for the build to succeed. If you are using Linux, some distributions split these off from the main Python package. Install python-dev or python-devel to get them.

Build/Install

Build and install as you would for any Python source repository. Download and extract a release or clone the repository, and run the following inside:

pip install .

Alternatively, you can have pip fetch and build from the latest source distribution on PyPI:

pip install --no-binary pymd4c pymd4c

Note that on Windows, setup.py assumes the MD4C library was installed at "C:/Program Files (x86)/MD4C/" (this is the default location when building MD4C from source, as described above). If this is not the case, installation will fail.

Class GenericParser

import md4c
generic_parser = md4c.GenericParser(parser_flags)

Initialize a new GenericParser. Parameters:

• parser_flags - An int made up of some combination of the parser option flags or'd together, e.g. md4c.MD_FLAG_TABLES | md4c.MD_FLAG_STRIKETHROUGH. For the default options, use 0, which will parse according to the base CommonMark specification. See the "Module-Wide Constants" section below for a full list of parser option flags.

Note: If the end goal of parsing is to produce HTML, strongly consider using an HTMLRenderer instead. All rendering will be performed by native C code, which will be much faster.

Parse Method

import md4c
generic_parser = md4c.GenericParser(...)
generic_parser.parse(input,
                     enter_block_callback,
                     leave_block_callback,
                     enter_span_callback,
                     leave_span_callback,
                     text_callback)

Parse markdown text using the provided callbacks. Parameters:

• input - A str or bytes containing the Markdown document to parse. If a bytes, it must be UTF-8 encoded.
• enter_block_callback - A function (or other callable) to be called whenever the parser enters a new block element in the Markdown source.
• leave_block_callback - A function (or other callable) to be called whenever the parser leaves a block element in the Markdown source.
• enter_span_callback - A function (or other callable) to be called whenever the parser enters a new inline element in the Markdown source.
• leave_span_callback - A function (or other callable) to be called whenever the parser leaves an inline element in the Markdown source.
• text_callback - A function (or other callable) to be called whenever the parser has text to add to the current block or inline element.

The parse() method will raise md4c.ParseError in the event of a problem during parsing, such as running out of memory. This does not signal invalid syntax, as there is no such thing in Markdown. It can also emit any exception raised by any of the callbacks (except md4c.StopParsing, which is caught and handled quietly).

Callback Details

enter_block_callback, leave_block_callback, enter_span_callback, and leave_span_callback all must accept two parameters:

• type - An md4c.BlockType or md4c.SpanType representing the type of block or span. See the "Enums" section for more info.

• details - A dict that contains extra information for certain types of blocks and spans, for example, the level of a heading. Keys are strs. Values are ints, single-character strs, or (for MD_ATTRIBUTE) lists of tuples or None.

  This dict will contain the information provided by MD_BLOCK_*_DETAIL and MD_SPAN_*_DETAIL structs in MD4C's md4c.h, with the following exceptions:

  • Non-task MD_BLOCK_LI blocks (when is_task is False) do not include task_mark and task_mark_offset keys.
  • Indented MD_BLOCK_CODE blocks do not include the fence_char key.

  Regarding MD_ATTRIBUTEs: These are used where a block or span can contain some associated text, such as link titles and code block language references. Such attributes may contain multiple text sub-elements (e.g. some regular text, an HTML entity, and then some more regular text). Thus, an MD_ATTRIBUTE value in details consists of a list of 2-tuples: (text_type, text) where text_type is an md4c.TextType (see "Enums" below) and text is the actual text as a str.

  Note that attributes may not always be provided. For example, an indented code block will not contain info or lang attributes. In those cases, the value will be None.

text_callback must also accept two parameters, but they are different:

• type - An md4c.TextType representing the type of text element. See the "Enums" section for more info.
• text - The actual text, as a str.

Callbacks need not return anything specific; their return values are ignored. To cancel parsing, callbacks can raise md4c.StopParsing. This will be caught by the parse() method and immediately halt parsing quietly. All other exceptions raised by callbacks will abort parsing and will be propagated back to the caller of parse().

Class HTMLRenderer

import md4c
html_renderer = md4c.HTMLRenderer(parser_flags, renderer_flags)

Initialize a new HTMLRenderer. Parameters:

• parser_flags - An int made up of some combination of the parser option flags or'd together, e.g. md4c.MD_FLAG_TABLES | md4c.MD_FLAG_STRIKETHROUGH. For the default options, use 0, which will parse according to the base CommonMark standard. See the "Module-Wide Constants" section below for a full list of parser option flags.
• renderer_flags - An int made up of some combination of the HTML renderer option flags or'd together. These are also listed in the "Module-Wide Constants" section below.

Parse Method

import md4c
html_renderer = md4c.HTMLRenderer(...)
output = html_renderer.parse(input)

Parse markdown text and return a str with rendered HTML. Parameters:

• input - A str or bytes containing the Markdown document to parse. If a bytes, it must be UTF-8 encoded.

This method will raise md4c.ParseError in the event of a problem during parsing, such as running out of memory. This does not signal invalid syntax, as there is no such thing in Markdown.

Module-Wide Constants

The MD4C library provides various option flags for parsers and renderers as named constants. These are made available as module-level constants in PyMD4C. Also, each constant has a correspondent optional keyword argument that can be used instanciating parser and renderers.

Parser Option Flags

Basic option flags:

md4c flag	keyword argument	description
md4c.MD_FLAG_COLLAPSEWHITESPACE	collapse_whitespace	In normal text, collapse non-trivial whitespace into a single space.
md4c.MD_FLAG_PERMISSIVEATXHEADERS	permissive_atx_headers	Do not requite a space in ATX headers (e.g. ###Header).
md4c.MD_FLAG_PERMISSIVEURLAUTOLINKS	permissive_url_autolinks	Convert URLs to links even without < and >.
md4c.MD_FLAG_PERMISSIVEEMAILAUTOLINKS	permissive_email_autolinks	Convert email addresses to links even without <, >, and mailto:.
md4c.MD_FLAG_NOINDENTEDCODEBLOCKS	no_indented_code_blocks	Disable indented code blocks (only allow fenced code blocks).
md4c.MD_FLAG_NOHTMLBLOCKS	no_html_blocks	Disable raw HTML blocks.
md4c.MD_FLAG_NOHTMLSPANS	no_html_spans	Disable raw HTML inlines.
md4c.MD_FLAG_TABLES	tables	Enable tables extension.
md4c.MD_FLAG_STRIKETHROUGH	strikethrough	Enable strikethrough extension.
md4c.MD_FLAG_PERMISSIVEWWWAUTOLINKS	permissive_www_autolinks	Enable www autolinks (even without any scheme prefix, as long as they begin with www.).
md4c.MD_FLAG_TASKLISTS	tasklists	Enable task lists extension.
md4c.MD_FLAG_LATEXMATHSPANS	latex_math_spans	Enable $ and $$ containing LaTeX equations.
md4c.MD_FLAG_WIKILINKS	wikilinks	Enable wiki links extension.
md4c.MD_FLAG_UNDERLINE	underline	Enable underline extension (and disable _ for regular emphasis).

Combination option flags:

md4c flag	keyword argument	description
md4c.MD_FLAG_PERMISSIVEAUTOLINKS	permissive_auto_links	Enables all varieties of autolinks: MD_FLAG_PERMISSIVEURLAUTOLINKS, MD_FLAG_PERMISSIVEEMAILAUTOLINKS, and MD_FLAG_PERMISSIVEWWWAUTOLINKS.
md4c.MD_FLAG_NOHTML	no_html	Disables all raw HTML tags: MD_FLAG_NOHTMLBLOCKS and MD_FLAG_NOHTMLSPANS.

Dialect option flags (note that not all features of a dialect may be supported, but these flags will cause MD4C to parse as many features of the dialect as it supports):

md4c flag	keyword argument	description
md4c.MD_DIALECT_GITHUB	dialect_github	Parse GitHub-Flavored Markdown, which enables the following flags: MD_FLAG_PERMISSIVEAUTOLINKS MD_FLAG_TABLES MD_FLAG_STRIKETHROUGH MD_FLAG_TASKLISTS

HTML Renderer Option Flags

md4c flag	keyword argument	description
md4c.MD_HTML_FLAG_DEBUG	debug	For development use, send MD4C debug output to stderr.
md4c.MD_HTML_FLAG_VERBATIM_ENTITIES	verbatim_entities	Do not replace HTML entities with the actual character (e.g. © with ©).
md4c.MD_HTML_FLAG_SKIP_UTF8_BOM	skip_utf8_bom	Omit BOM from start of UTF-8 input.
md4c.MD_HTML_FLAG_XHTML	xhtml	Generate XHTML instead of HTML.

Enums

The MD4C library uses various enums to provide data to callbacks. PyMD4C uses IntEnums to encapsulate these.

See md4c.h from the MD4C project for more information on these enums and associated types.

Block Types - class BlockType

• md4c.BlockType.DOC - Document
• md4c.BlockType.QUOTE - Block quote
• md4c.BlockType.UL - Unordered list
• md4c.BlockType.OL - Ordered list
• md4c.BlockType.LI - List item
• md4c.BlockType.HR - Horizontal rule
• md4c.BlockType.H - Heading
• md4c.BlockType.CODE - Code block
• md4c.BlockType.HTML - Raw HTML block
• md4c.BlockType.P - Paragraph
• md4c.BlockType.TABLE - Table
• md4c.BlockType.THEAD - Table header row
• md4c.BlockType.TBODY - Table body
• md4c.BlockType.TR - Table row
• md4c.BlockType.TH - Table header cell
• md4c.BlockType.TD - Table cell

Span Types - class SpanType

• md4c.SpanType.EM - Emphasis
• md4c.SpanType.STRONG - Strong
• md4c.SpanType.A - Link
• md4c.SpanType.IMG - Image
• md4c.SpanType.CODE - Inline code
• md4c.SpanType.DEL - Strikethrough
• md4c.SpanType.LATEXMATH - Inline math
• md4c.SpanType.LATEXMATH_DISPLAY - Display math
• md4c.SpanType.WIKILINK - Wiki link
• md4c.SpanType.U - Underline

Text Types - class TextType

• md4c.TextType.NORMAL - Normal text
• md4c.TextType.NULLCHAR - NULL character
• md4c.TextType.BR - Line break
• md4c.TextType.SOFTBR - Soft line break
• md4c.TextType.ENTITY - HTML Entity
• md4c.TextType.CODE - Text inside a code block or inline code
• md4c.TextType.HTML - Raw HTML (inside an HTML block or simply inline HTML)
• md4c.TextType.LATEXMATH - Text inside an equation

Table Alignments - class Align

• md4c.Align.DEFAULT
• md4c.Align.LEFT
• md4c.Align.CENTER
• md4c.Align.RIGHT

Exceptions

• md4c.ParseError - Raised by one of the parse() methods when there is an error during parsing, such as running out of memory. There is no such thing as invalid syntax in Markdown, so this really only signals some sort of system error.

• md4c.StopParsing - A callback can raise this to stop parsing early. GenericParser's parse() method will catch it and abort quietly.

License

This project is licensed under the MIT license. See the LICENSE.md file for details.