subclass string.Formatter

Question

Following a remark here: How to define a new string formatter, I tried subclassing string.Formatter. Here is what I\'ve done. Unfortunately I seem to have broke

Answer 1

Good news: you have not done anything wrong. Bad news: that's how string.Formatter behaves, it does not support {}-like positional format. So, the last call will fail even without any subclassing. Good news: that's can be fixed by overriding the parse method:

import string

class CF(string.Formatter):
    def parse(self, s):
        position = 0
        for lit, name, spec, conv in super(CF, self).parse(s):
            if not name:
                name = str(position)
                position += 1
            yield lit, name, spec, conv

Bad news... Ah, no, that's basically it:

>>> CF().format('{} {}!', 'Hello', 'world')
'Hello world!'