[Python-Dev] [Python-ideas] Proposed addtion to urllib.parse in 3.1 (and urlparse in 2.7)

[Mart Sõmermaa]

On Sun, Apr 19, 2009 at 2:06 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> That said, I'm starting to wonder if an even better option may be to
> just drop the kwargs support from the function and require people to
> always supply a parameters dictionary. That would simplify the signature
> to the quite straightforward:
>
>  def add_query_params(url, params, allow_dups=True, sep='&')

That's the most straightforward and I like this more than the one below.

> I agree that isn't a good option, but mapping True/False/None to those
> specific behaviours also seems rather arbitrary (specifically, it is
> difficult to remember which of "allow_dups=False" and "allow_dups=None"
> means to ignore any duplicate keys and which means to ignore only
> duplicate items).

I'd say it's less of a problem when using named arguments, i.e. you read it as:

allow_dups=True : yes
allow_dups=False : effeminately no :),
allow_dups=None : strictly no

which more or less corresponds to the behaviour.

> It also doesn't provide a clear mechanism for
> extension (e.g. what if someone wanted duplicate params to trigger an
> exception?)
>
> Perhaps the extra argument should just be a key/value pair filtering
> function, and we provide functions for the three existing behaviours
> (i.e. allow_duplicates(), ignore_duplicate_keys(),
> ignore_duplicate_items()) in the urllib.parse module.

This would be the most flexible and conceptually right (ye olde
strategy pattern), but would clutter the API.

> Note that your implementation and docstring currently conflict with each
> other - the docstring says "pass them via a dictionary in second
> argument:" but the dictionary is currently the third argument (the
> docstring also later refers to passing OrderedDictionary as the second
> argument).

It's a mistake that exemplifies once again that positional args are awkward :).

---

So, gentlemen, either

def add_query_params(url, params, allow_dups=True, sep='&')

or

def allow_duplicates(...)

def remove_duplicate_values(...)

...

def add_query_params(url, params, strategy=allow_duplicates, sep='&')