I'm looking to try and keep pluralisation of existing strings as simple as possible, and was wondering if it was possible to get `str.format()` to interpret a default value when looking for kwargs. Here's an example:

```
string = "{number_of_sheep} sheep {has} run away"
dict_compiled_somewhere_else = {'number_of_sheep' : 4, 'has' : 'have'}

string.format(**dict_compiled_somewhere_else)
# gives "4 sheep have run away"

other_dict = {'number_of_sheep' : 1}
string.format(**other_dict)
# gives a key error: u'has'
# What I'd like is for format to somehow default to the key, or perhaps have some way of defining the 'default' value for the 'has' key 
# I'd have liked: "1 sheep has run away"

```

Cheers