Python Essential Reference, Second Edition

Operations on Dictionaries

Dictionaries provide a mapping between names and objects. You can apply the following operations to dictionaries:

Operation	Description
x = d [k ]	Indexing by key
d [k ] = x	Key assignment
del d [k ]	Deletes an item by key
len(d )	Number of items in the dictionary

Key values can be any immutable object, such as strings, numbers, and tuples. In addition, dictionary keys can be specified as a comma-separated list of values like this:

d = { } 
d[1,2,3] = "foo" 
d[1,0,3] = "bar" 

In this case, the key values represent a tuple, making the above assignments identical to the following:

d[(1,2,3)] = "foo" 
d[(1,0,3)] = "bar"