Example of python filter involving pandocfilters.Link

Example of python filter involving pandocfilters.Link

[camille.huguenot-Re5JQEeQqe8AvxtiuMwx3w]

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Dear developers and users of pandoc,

  I could not find an example of a python filter manipulating the 'Link' 
constructor. Could someone point me to such an example ? I'm a poor python 
developer and debugging filters isn't very handy :-/ I'm trying to write a 
filter that automatically adds the .html extension to targets of links if 
missing (so as to avoid depending on the output format in our markdown 
sources).

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Re: Example of python filter involving pandocfilters.Link

[John MacFarlane]

value[0] will be the link label (a list of inline elements).
value[1] is the "target".  It is itself an array containing URL and
title.  So, value[1][0] will be the URL.  value[1][1] will be the title.

You'll need to modify value[1][0], then return

Link(value[0], value[1])

Something like this:

from pandocfilters import toJSONFilter, Link

def add_html(key, value, format, meta):
   if key == 'Link':
     value[1][0] = value[1][0] + ".html"
     return Link(value[0], value[1])

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

Hope that helps.  Apologies that the python library is not better
designed or better documented.  The translation from Haskell types
to python is automatic, and once you get the hang of it you can use
the definitions in Text.Pandoc.Definition as documentation.

+++ camille.huguenot-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org [Apr 15 14 06:47 ]:
>   Dear developers and users of pandoc,
>     I could not find an example of a python filter manipulating the
>   'Link' constructor. Could someone point me to such an example ? I'm a
>   poor python developer and debugging filters isn't very handy :-/ I'm
>   trying to write a filter that automatically adds the .html extension to
>   targets of links if missing (so as to avoid depending on the output
>   format in our markdown sources).
>
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Re: Example of python filter involving pandocfilters.Link

[camille.huguenot-Re5JQEeQqe8AvxtiuMwx3w]

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Thanks John. For those interested (I guess this script is a common 
request), here's the script that handles anchors and distant links:

#!/usr/bin/env python

"""
Pandoc filter to add ".html" to links when outputting html (if missing)
"""

import pandocfilters # provided by 
https://pypi.python.org/pypi/pandocfilters 

def link(key, value, format, meta):
        # Add .html to links that do not have it
    if key == 'Link' and (format == "html" or format == "html5"):
        # From John MacFarlane (pandoc 1.12):
        # value[0] is the link label (a list of inline elements).
        # value[1] is the "target".  It is itself an array containing URL 
and
        # title. So, value[1][0] is the URL. value[1][1] is the title. 
        url=value[1][0]
        if url.startswith("http") or url.startswith("www"):
            # A distant link, not touching it
            return

        # A local link (if markdown files have the convention to prefix 
distant link as tested above)
        idx=url.rfind('#')
        if 0 == idx:
            # There's an anchor in the first position! It refers to
            # the current file, not adding ".html" before it, it's useless 
and
            # would produce wrong html
            pass
        elif 0 < idx:
            # There's an anchor! If ".html" is missing before '#' we add it.
            head=url[0:idx]
            tail=url[idx+1:len(url)]
            if not head.endswith(".html"):
                # The extension is missing, let's add it
                value[1][0] = head+".html#"+tail
                return pandocfilters.Link(value[0], value[1])
        elif not url.endswith(".html"):
            # The extension is missing, let's add it
            value[1][0] = url+".html"
            return pandocfilters.Link(value[0], value[1])

if __name__ == "__main__":
    pandocfilters.toJSONFilter(link)

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Re: Example of python filter involving pandocfilters.Link

[Ben White]

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I am using pandoc 1.16.0.2 with the python pandoc filters. I noticed that 
the Link constructor now takes 3 parameters, so the above is not valid for 
this version. Does anybody know what the parameters should be now? Thx

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Re: Example of python filter involving pandocfilters.Link

[Sergio Correia]

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You can see the definitions here:
https://github.com/jgm/pandoc-types/blob/master/Text/Pandoc/Definition.hs#L264

So you would do *Link(attributes, label, target)*, with *attributes* the 
new argument.

You can also see this with a quick call to pandoc:

*>echo [Link](url "title"){.class x=123 #id} | pandoc --to=native*
*[Para [Link ("id",["class"],[("x","123")]) [Str "Link"] ("url","title")]]*

I'm not 100% sure, but if you don't want anything in attributes, you could 
just add

*attributes = ["",[],[]]*

And then create *Link(attributes, ...)*

On Wednesday, January 4, 2017 at 4:29:18 AM UTC-5, Ben White wrote:
>
> I am using pandoc 1.16.0.2 with the python pandoc filters. I noticed that 
> the Link constructor now takes 3 parameters, so the above is not valid for 
> this version. Does anybody know what the parameters should be now? Thx
>

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Re: Example of python filter involving pandocfilters.Link

[Ben White]

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That's really useful, thanks a lot.

Spent some time digging about in the haddock docs to find the type defs, 
but the source in the link is easier to figure out.

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