Re: [Python-markdown-discuss] Python-markdown extension API

[Hendra <hen...@gm...>]

Even when the extension is initialized like the one in this example?

http://pythonhosted.org/Markdown/extensions/api.html#makeextension

import markdown
import myextension
configs = {...}
myext = myextension.MyExtension(configs=configs)
md = markdown.Markdown(extensions=[myext])

In that snippet, `configs` is passed, but it seems possible to initialize
MyExtension without any argument.

On Sun, Jun 23, 2013 at 9:34 PM, Waylan Limberg <wa...@gm...> wrote:

> Actually, the way the Markdown class calls extensions, None will never
> be passed as a value for configs. Markdown always sets a default value
> to pass in, so technically, your extension doesn't need to worry about
> setting a default value.
>
> Otherwise you would be correct. `foo = dict(arg) or {}` would throw an
> error if arg was None.
> ----
> \X/ /-\ `/ |_ /-\ |\|
> Waylan Limberg
>
>
> On Sun, Jun 23, 2013 at 1:19 AM, Hendra <hen...@gm...> wrote:
> >
> > Ah, I see.. Pretty nasty gotcha..
> > But then, in that case, in the wikilinks example, shouldn't the
> assignment
> > be this way:
> >
> > if configs is None:
> >     configs = {}
> > else:
> >     configs = dict(configs)
> >
> > Wouldn't dict(None) throw a TypeError as well? And since the constructor
> of
> > the WikiLinkExtension doesn't have default value for the `configs`
> > parameter, does that mean it must always receive an argument?
> > Or did I misunderstood the whole extension API itself?
> >
> >
> > On Sun, Jun 23, 2013 at 12:34 PM, Waylan Limberg <wa...@gm...>
> wrote:
> >>
> >> A dict is a mutable object, so you should never assign it as a default
> >> to an argument. See this [1] for one of the many explanations out
> >> there.
> >>
> >> We avoid the TypeError with a line like this inside a function/method:
> >>
> >>     foo = arg or {}
> >>
> >> The above is shorthand for:
> >>
> >>     if arg:             # If arg is None this evaluates to false
> >>         foo = arg    # only use arg when a value was passed in
> >>     else:
> >>         foo = {}       # avoid a TypeError here
> >>
> >> Now the only way to get a TypeError is if the user passes in a bad
> >> type -- unless that type would evaluate to false -- in which case the
> >> default would be used.
> >>
> >> This is basic Python. Eventually you'll get it. In fact, I  couldn't
> >> remember what the reason was offhand. I knew it was wrong to assign a
> >> dict as a default, but had to do a search to remember why.
> >>
> >> [1]: http://effbot.org/zone/default-values.htm
> >> ----
> >> \X/ /-\ `/ |_ /-\ |\|
> >> Waylan Limberg
> >>
> >>
> >> On Sat, Jun 22, 2013 at 11:15 PM, Hendra <hen...@gm...> wrote:
> >> > I see,, thanks, that helps a lot. Should've checked out that one.
> >> >
> >> > Another question, hope this doesn't sound stupid. Why is the default
> >> > argument value for `configs` that is passed to the `makeExtension` is
> >> > `None`, instead of `{}`? wouldn't that cause a TypeError?
> >> >
> >> >
> >> > On Sat, Jun 22, 2013 at 10:29 PM, Waylan Limberg <wa...@gm...>
> >> > wrote:
> >> >>
> >> >> Hendra,
> >> >>
> >> >> Take a look at the wikilinks extension [1]. It makes extensive use of
> >> >> configs. Note that some defaults are set first (line 95) in a dict.
> >> >> Then the user provided settings are forced to a dict (line 101)
> >> >> (`dict()` will convert a list of tuples to a dict or if passed a
> dict,
> >> >> will simply return it). Finally, the settings are iterated over (line
> >> >> 103), overriding the already set defaults (104).
> >> >>
> >> >> So, to answer your question, either a list of tuples or a dict can be
> >> >> passed in as settings. Either way, it will be stored as a dict if you
> >> >> use the config methods on the `markdown.extensions.Extension` class.
> >> >> Of course, as you are subclassing, you can override config handling
> if
> >> >> you want to make it work however you would like.
> >> >>
> >> >> Hope that helps.
> >> >>
> >> >> [1]:
> >> >>
> >> >>
> https://github.com/waylan/Python-Markdown/blob/master/markdown/extensions/wikilinks.py
> >> >> ----
> >> >> \X/ /-\ `/ |_ /-\ |\|
> >> >> Waylan Limberg
> >> >>
> >> >>
> >> >> On Sat, Jun 22, 2013 at 9:03 AM, Hendra <hen...@gm...>
> wrote:
> >> >> > Hi,
> >> >> > I am trying to write a simple extension for the python markdown
> API,
> >> >> > but
> >> >> > I
> >> >> > am having some problem with setting the config. From the doc:
> >> >> >
> >> >> > import markdown
> >> >> > import myextension
> >> >> > configs = {...}
> >> >> > myext = myextension.MyExtension(configs=configs)
> >> >> > md = markdown.Markdown(extensions=[myext])
> >> >> >
> >> >> > It seems like I would have to pass the config in a dict, but when I
> >> >> > try
> >> >> > to
> >> >> > initialize the extension with the name of the extension, it
> receives
> >> >> > the
> >> >> > config as a list (I am guessing from config.items() ).
> >> >> >
> >> >> > Looking around the source of the extensions here:
> >> >> >
> >> >> >
> >> >> >
> https://github.com/waylan/Python-Markdown/tree/master/markdown/extensions,
> >> >> > it seems like in most of them, configs is a list. So, which is the
> >> >> > right
> >> >> > one?
> >> >> >
> >> >> >
> >> >> > --
> >> >> > Best Regards, and Thank you,
> >> >> > Hendra
> >> >> >
> >> >> >
> >> >> >
> >> >> >
> ------------------------------------------------------------------------------
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> >> >> > _______________________________________________
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> >> >> >
> https://lists.sourceforge.net/lists/listinfo/python-markdown-discuss
> >> >> >
> >> >
> >> >
> >> >
> >> >
> >> > --
> >> > Best Regards, and Thank you,
> >> > Hendra
> >
> >
> >
> >
> > --
> > Best Regards, and Thank you,
> > Hendra
>



-- 
Best Regards, and Thank you,
Hendra