Core Python Programming (2nd Edition)

[d] New in Python 2.2.
[e] New in Python 2.0.
Below, we showcase some of the more common dictionary methods. We have already seen has_key()
and its replacements in and not in at work above. Attempting to access a nonexistent key will result in
an exception (KeyError) as we saw in Section 7.1.
Basic dictionary methods focus on their keys and values. These are keys(), which returns a list of the
dictionary's keys, values(), which returns a list of the dictionary's values, and items(), which returns a
list of (key, value) tuple pairs. These are useful when you wish to iterate through a dictionary's keys or
values, albeit in no particular order.
>>> dict2.keys()
['port', 'name']
>>>
>>> dict2.values()
[80, 'earth']
>>>
>>> dict2.items()
[('port', 80), ('name', 'earth')]
>>>
>>> for eachKey in dict2.keys():
... print 'dict2 key', eachKey, 'has value', dict2[eachKey]
...
dict2 key port has value 80
dict2 key name has value earth
The keys() method is fairly useful when used in conjunction with a for loop to retrieve a dictionary's
values as it returns a list of a dictionary's keys. However, because its items (as with any keys of a hash
table) are unordered, imposing some type of order is usually desired.
In Python versions prior to 2.4, you would have to call a dictionary's keys() method to get the list of its
keys, then call that list's sort() method to get a sorted list to iterate over. Now a built-in function
named sorted(), made especially for iterators, exists, which returns a sorted iterator:
>>> for eachKey in sorted(dict2):
... print 'dict2 key', eachKey, 'has value',
dict2[eachKey]
...
dict2 key name has value earth
dict2 key port has value 80
The update() method can be used to add the contents of one directory to another. Any existing entries
with duplicate keys will be overridden by the new incoming entries. Nonexistent ones will be added. All
entries in a dictionary can be removed with the clear() method.