python string format() with dict with integer keys [duplicate]

Question

I would like to use Python string's format() to act as a quick and dirty template. However, the dict that I would like to use has keys which are (string representations) of integers. a simplified example follows:

s = 'hello there {5}'
d = {'5': 'you'}
s.format(**d)

the above code throws the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: tuple index out of range

is it possible to do the above?

Answer 1

We've established that it won't work, but how about a solution:

Although str.format won't work in this case, funnily enough the old % formatting will. This is not recommended, but you did ask for a quick and dirty template.

>>> 'hello there %(5)s' % {'5': 'you'}
'hello there you'

Do note though that this won't work for integer keys.

>>> 'hello there %(5)s' % {5: 'you'}

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    'hello there %(5)s' % {5: 'you'}
KeyError: '5'

Answer 2

I love the idea of extending the Formatter so that it allows arbitrary field names (integers, field names with a colon etc). An implementation might look like this:

import string, re

class QuFormatter(string.Formatter):
    def _quote(self, m):
        if not hasattr(self, 'quoted'):
            self.quoted = {}
        key = '__q__' + str(len(self.quoted))
        self.quoted[key] = m.group(2)
        return '{' + m.group(1) + key + m.group(3) + '}'

    def parse(self, format_string):
        return string.Formatter.parse(self,
            re.sub(r'{([^}`]*)`([^}`]*)`([^}]*)}', self._quote, format_string))

    def get_value(self, key, args, kwargs):
        if key.startswith('__q__'):
            key = self.quoted[key]
        return string.Formatter.get_value(self, key, args, kwargs)

Usage:

d = {'5': 'you', '6': 'me', "okay":1, "weird:thing!": 123456}
print QuFormatter().format(
     'hello there {`5`} {`6`:20s}--{okay}--{`weird:thing!`:20,d}', 
     **d)

So fields in backticks are treated literally.