KeyError

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Python raises a KeyError whenever a dict() object is requested (using the format a = adict[key]) and the key is not in the dictionary.

If you don't want to have an exception but would rather a default value used instead, you can use the get() method:

   1 default = 'Scruffy'
   2 a = adict.get('dogname', default)

Even more handy is somewhat controversially-named setdefault(key, val) which sets the value of the key only if it is not already in the dict, and returns that value in any case:

   1 default = 'Scruffy'
   2 dog_owned_by = {'Peter': 'Furry', 'Sally': 'Fluffy'}
   3 
   4 dogs = []
   5 for owner in ('Peter', 'Sally', 'Tim'):
   6     dogs.append(dog_owned_by.setdefault(owner, default))
   7 
   8 
   9