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

[Waylan L. <wa...@gm...>]

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