pandocfilters

A python module for writing pandoc <http://pandoc.org/>_ filters

What are pandoc filters?

Pandoc filters
are pipes that read a JSON serialization of the Pandoc AST
from stdin, transform it in some way, and write it to stdout.
They can be used with pandoc (>= 1.12) either using pipes ::

pandoc -t json -s | ./caps.py | pandoc -f json

or using the --filter (or -F) command-line option. ::

pandoc --filter ./caps.py -s

For more on pandoc filters, see the pandoc documentation under --filter
and the tutorial on writing filters__.

__ http://johnmacfarlane.net/pandoc/scripting.html

For an alternative library for writing pandoc filters, with
a more "Pythonic" design, see panflute__.

__ https://github.com/sergiocorreia/panflute

Compatibility

Pandoc 1.16 introduced link and image attributes to the existing
caption and target arguments, requiring a change in pandocfilters
that breaks backwards compatibility. Consequently, you should use:

pandocfilters version <= 1.2.4 for pandoc versions 1.12--1.15, and
pandocfilters version >= 1.3.0 for pandoc versions >= 1.16.

Pandoc 1.17.3 (pandoc-types 1.17.*) introduced a new JSON format.
pandocfilters 1.4.0 should work with both the old and the new
format.

Installing

Run this inside the present directory::

python setup.py install

Or install from PyPI::

pip install pandocfilters

Available functions

The main functions pandocfilters exports are

walk(x, action, format, meta)

Walk a tree, applying an action to every object. Returns a modified
tree. An action is a function of the form
action(key, value, format, meta), where:
- key is the type of the pandoc object (e.g. 'Str', 'Para')
- value is the contents of the object (e.g. a string for 'Str', a list of
  inline elements for 'Para')
- format is the target output format (as supplied by the
  format argument of walk)
- meta is the document's metadata
The return of an action is either:
- None: this means that the object should remain unchanged
- a pandoc object: this will replace the original object
- a list of pandoc objects: these will replace the original object;
  the list is merged with the neighbors of the original objects
  (spliced into the list the original object belongs to); returning
  an empty list deletes the object
toJSONFilter(action)

Like toJSONFilters, but takes a single action as argument.
toJSONFilters(actions)

Generate a JSON-to-JSON filter from stdin to stdout

The filter:
- reads a JSON-formatted pandoc document from stdin
- transforms it by walking the tree and performing the actions
- returns a new JSON-formatted pandoc document to stdout
The argument actions is a list of functions of the form
action(key, value, format, meta), as described in more detail
under walk.

This function calls applyJSONFilters, with the format
argument provided by the first command-line argument, if present.
(Pandoc sets this by default when calling filters.)
applyJSONFilters(actions, source, format="")

Walk through JSON structure and apply filters

This:
- reads a JSON-formatted pandoc document from a source string
- transforms it by walking the tree and performing the actions
- returns a new JSON-formatted pandoc document as a string
The actions argument is a list of functions (see walk for a
full description).

The argument source is a string encoded JSON object.

The argument format is a string describing the output format.

Returns a new JSON-formatted pandoc document.
stringify(x)

Walks the tree x and returns concatenated string content, leaving out
all formatting.
attributes(attrs)

Returns an attribute list, constructed from the dictionary attrs.

How to use

Most users will only need toJSONFilter. Here is a simple example
of its use::

#!/usr/bin/env python

"""
Pandoc filter to convert all regular text to uppercase.
Code, link URLs, etc. are not affected.
"""

from pandocfilters import toJSONFilter, Str

def caps(key, value, format, meta):
  if key == 'Str':
    return Str(value.upper())

if __name__ == "__main__":
  toJSONFilter(caps)

Examples

The examples subdirectory in the source repository contains the
following filters. These filters should provide a useful starting point
for developing your own pandocfilters.

abc.py
Pandoc filter to process code blocks with class abc containing ABC
notation into images. Assumes that abcm2ps and ImageMagick's convert
are in the path. Images are put in the abc-images directory.

caps.py
Pandoc filter to convert all regular text to uppercase. Code, link
URLs, etc. are not affected.

blockdiag.py
Pandoc filter to process code blocks with class "blockdiag" into
generated images. Needs utils from http://blockdiag.com.

comments.py
Pandoc filter that causes everything between
 and  to be ignored.
The comment lines must appear on lines by themselves, with blank
lines surrounding

deemph.py
Pandoc filter that causes emphasized text to be displayed in ALL
CAPS.

deflists.py
Pandoc filter to convert definition lists to bullet lists with the
defined terms in strong emphasis (for compatibility with standard
markdown).

gabc.py
Pandoc filter to convert code blocks with class "gabc" to LaTeX
\gabcsnippet commands in LaTeX output, and to images in HTML output.

graphviz.py
Pandoc filter to process code blocks with class graphviz into
graphviz-generated images.

lilypond.py
Pandoc filter to process code blocks with class "ly" containing
Lilypond notation.

metavars.py
Pandoc filter to allow interpolation of metadata fields into a
document. %{fields} will be replaced by the field's value, assuming
it is of the type MetaInlines or MetaString.

myemph.py
Pandoc filter that causes emphasis to be rendered using the custom
macro \myemph{...} rather than \emph{...} in latex. Other output
formats are unaffected.

plantuml.py
Pandoc filter to process code blocks with class plantuml to images.
Needs plantuml.jar from http://plantuml.com/.

ditaa.py
Pandoc filter to process code blocks with class ditaa to images.
Needs ditaa.jar from http://ditaa.sourceforge.net/.

theorem.py
Pandoc filter to convert divs with class="theorem" to LaTeX theorem
environments in LaTeX output, and to numbered theorems in HTML
output.

tikz.py
Pandoc filter to process raw latex tikz environments into images.
Assumes that pdflatex is in the path, and that the standalone
package is available. Also assumes that ImageMagick's convert is in
the path. Images are put in the tikz-images directory.

API documentation

By default most filters use get_filename4code to
create a directory ...-images to save temporary
files. This directory doesn't get removed as it can be used as a cache so that
later pandoc runs don't have to recreate files if they already exist. The
directory is generated in the current directory.

If you prefer to have a clean directory after running pandoc filters, you
can set an environment variable PANDOCFILTER_CLEANUP to any non-empty value such as 1
which forces the code to create a temporary directory that will be removed
by the end of execution.

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