String format - resolve placeholders names

[Chris Angelico]

On Sat, Nov 21, 2015 at 1:52 AM, Ervin Hegedüs <airween at gmail.com> wrote:
> Python has a good string formatter, eg. I can do this:
>
> s = "{who} likes {what}"
> d = {'who': "Adam", 'what': "ants"}
> s.format(**d)
>
> result:
> 'Adam likes ants'
>
> Is it possible, and if yes, how to resolve the placeholders names
> in string?
>
> There is a know method:
>
> d1 = {'who1': "Adam", 'what1': "ants"}
> try:
>     s.format(**d1)
> except KeyError:
>     print("keyword missing")
>
> (gives 'keyword missing' as result).
>
>
> But is there any other (direct) way, which keywords exists in
> string?

I think what you're asking for can be done using format_map with a
custom mapping object:

>>> class IdentiMap:
...     def __init__(self):
...         self.keys = []
...     def __getitem__(self, key):
...         self.keys.append(key)
...
>>> m = IdentiMap()
>>> "{who} likes {what}".format_map(m)
'None likes None'
>>> m.keys
['who', 'what']

Does that help?

ChrisA