python - String format with optional dict key-value

Question

Is there any way to format string with dict but optionally without key errors?

This works fine:

opening_line = '%(greetings)s  %(name)s !!!'
opening_line % {'greetings': 'hello', 'name': 'john'}

But let's say I don't know the name, and I would like to format above line only for 'greetings'. Something like,

 opening_line % {'greetings': 'hello'}

Output would be fine even if:

'hii %(name)s !!!'  # keeping name un-formatted 

But this gives KeyError while unpacking

Is there any way?

Answer 1

Use defaultdict, this will allow you to specify a default value for keys which don't exist in the dictionary. For example:

>>> from collections import defaultdict
>>> d = defaultdict(lambda: 'UNKNOWN')
>>> d.update({'greetings': 'hello'})
>>> '%(greetings)s  %(name)s !!!' % d
'hello  UNKNOWN !!!'
>>>