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String format with optional key value

Is it possible to format a string using dict, but not necessarily without key errors?

This works great:

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

But let me say that I do not know the name, and I would like to format the above strings only for 'greetings' . Sort of,

  opening_line % {'greetings': 'hello'}

The output would be accurate even if:

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

But this gives a KeyError when unpacking

Is there any way?

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3 answers

Use defaultdict , this will allow you to specify a default value for keys that are not in the dictionary. For instance:

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

 greeting_dict = {'greetings': 'hello'} if 'name' in greeting_dict : opening_line = '{greetings} {name}'.format(**greeting_dict) else: opening_line = '{greetings}'.format(**greeting_dict) print opening_line

Perhaps even more succinctly, use the dictionary to set the default for each parameter,

 '{greetings} {name}'.format(greetings=greeting_dict.get('greetings','hi'), name=greeting_dict.get('name',''))
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For the record:

 info = { 'greetings':'DEFAULT', 'name':'DEFAULT', } opening_line = '{greetings} {name} !!!' info['greetings'] = 'Hii' print opening_line.format(**info) # Hii DEFAULT !!!
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