Dictionary

Dictionaries are mutable ordered data type:

• data in dictionary are pairs key: value

• values are accessible by key, not by number as in lists

• entries in dictionary stored in order they were added

• since dictionaries are mutable, dictionary items can be changed, added, removed

• key must be an immutable object: number, string, tuple

• value can be data of any type

Note

In other programming languages a similar dictionary can be called an associative array, hash, or hash table.

Example of dictionary:

london = {'name': 'London1', 'location': 'London Str', 'vendor': 'Cisco'}

You can write it down like this:

london = {
    'id': 1,
    'name': 'London',
    'it_vlan': 320,
    'user_vlan': 1010,
    'mngmt_vlan': 99,
    'to_name': None,
    'to_id': None,
    'port': 'G1/0/11'
}

In order to get a value from dictionary you have to refer to key in the same way as in lists, only key will be used instead of number:

In [1]: london = {'name': 'London1', 'location': 'London Str'}

In [2]: london['name']
Out[2]: 'London1'

In [3]: london['location']
Out[3]: 'London Str'

Similarly, a new key-value pair could be added:

In [4]: london['vendor'] = 'Cisco'

In [5]: print(london)
{'vendor': 'Cisco', 'name': 'London1', 'location': 'London Str'}

Or rewritten:

In [6]: london['vendor'] = 'cisco ios'

In [7]: print(london)
{'vendor': 'cisco ios', 'name': 'London1', 'location': 'London Str'}

In dictionary you can use a dictionary as a value:

london_co = {
    'r1': {
        'hostname': 'london_r1',
        'location': '21 New Globe Walk',
        'vendor': 'Cisco',
        'model': '4451',
        'ios': '15.4',
        'ip': '10.255.0.1'
    },
    'r2': {
        'hostname': 'london_r2',
        'location': '21 New Globe Walk',
        'vendor': 'Cisco',
        'model': '4451',
        'ios': '15.4',
        'ip': '10.255.0.2'
    },
    'sw1': {
        'hostname': 'london_sw1',
        'location': '21 New Globe Walk',
        'vendor': 'Cisco',
        'model': '3850',
        'ios': '3.6.XE',
        'ip': '10.255.0.101'
    }
}

You can get values from nested dictionary by:

In [7]: london_co['r1']['ios']
Out[7]: '15.4'

In [8]: london_co['r1']['model']
Out[8]: '4451'

In [9]: london_co['sw1']['ip']
Out[9]: '10.255.0.101'

Function sorted sorts dictionary keys in ascending order and returns a new list with sorted keys:

In [1]: london = {'name': 'London1', 'location': 'London Str', 'vendor': 'Cisco'}

In [2]: sorted(london)
Out[2]: ['location', 'name', 'vendor']