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

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

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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> >> >
> >
> >
> >
> >
> > --
> > Best Regards, and Thank you,
> > Hendra
>



-- 
Best Regards, and Thank you,
Hendra