Core Python Programming (2nd Edition)

dict2 = {'name': 'earth', 'port': 80}
>>>
>>>> for key in dict2.keys():
... print 'key=%s, value=%s' % (key, dict2[key])
...
key=name, value=earth
key=port, value=80
Beginning with Python 2.2, you no longer need to use the keys() method to extract a list of keys to loop
over. Iterators were created to simplify accessing of sequence-like objects such as dictionaries and files.
Using just the dictionary name itself will cause an iterator over that dictionary to be used in a for loop:
>>> dict2 = {'name': 'earth', 'port': 80}
>>>
>>>> for key in dict2:
... print 'key=%s, value=%s' % (key, dict2[key])
...
key=name, value=earth
key=port, value=80
To access individual dictionary elements, you use the familiar square brackets along with the key to
obtain its value:
>>> dict2['name']
'earth'
>>>
>>> print 'host %s is running on port %d' % \
... (dict2['name'], dict2['port'])
host earth is running on port 80
Dictionary dict1 defined above is empty while dict2 has two data items. The keys in dict2 are 'name'
and 'port', and their associated value items are 'earth' and 80, respectively. Access to the value is
through the key, as you can see from the explicit access to the 'name' key.
If we attempt to access a data item with a key that is not part of the dictionary, we get an error:
>>> dict2['server']
Traceback (innermost last):
File "", line 1, in ?
KeyError: server
In this example, we tried to access a value with the key 'server' which, as you know from the code
above, does not exist. The best way to check if a dictionary has a specific key is to use the dictionary's
has_key() method, or better yet, the in or not in operators starting with version 2.2. The has_key()
method will be obsoleted in future versions of Python, so it is best to just use in or not in.