partial string formatting

Question

Is it possible to do partial string formatting with the advanced string formatting methods, similar to the string template safe_substitute() function?

F

Answer 1

Not sure if this is ok as a quick workaround, but how about

s = '{foo} {bar}'
s.format(foo='FOO', bar='{bar}')

? :)

Answer 2

There is one more way to achieve this i.e by using format and % to replace variables. For example:

>>> s = '{foo} %(bar)s'
>>> s = s.format(foo='my_foo')
>>> s
'my_foo %(bar)s'
>>> s % {'bar': 'my_bar'}
'my_foo my_bar'

Answer 3

Thanks to Amber's comment, I came up with this:

import string

try:
    # Python 3
    from _string import formatter_field_name_split
except ImportError:
    formatter_field_name_split = str._formatter_field_name_split


class PartialFormatter(string.Formatter):
    def get_field(self, field_name, args, kwargs):
        try:
            val = super(PartialFormatter, self).get_field(field_name, args, kwargs)
        except (IndexError, KeyError, AttributeError):
            first, _ = formatter_field_name_split(field_name)
            val = '{' + field_name + '}', first
        return val