Python Collections

Python Collections at a Glance

Collections keep related values together. Choose the structure according to whether order matters, values may change, or each value needs a descriptive key.

1. Collection Data Types

A collection keeps related values together. A list can hold devices waiting to be checked. A tuple can hold fixed interface details. A dictionary can describe one device with names such as ip, model, and site.

2. Python Lists

A list is an ordered group that can change. Use it when items may be added, removed, or updated while the script runs.

>>> router_ip_addresses = ["192.168.1.1", "192.168.1.2", "192.168.1.3"]
>>> switch_ip_addresses = ["172.16.1.1", "172.16.1.2", "172.16.1.3"]
>>> my_numbers = [1, 2, 3, 4, 5, 6]
>>> random_stuff = ["R1", 5, "SW1", 7]

List positions start at 0, so index 0 selects the first item. Index -1 selects the last item.

>>> ips = ["192.168.1.1", "192.168.1.2", "192.168.1.3"]
>>> ips[0]
'192.168.1.1'
>>> ips[-1]
'192.168.1.3'

3. List Operations

Use append() to add an item. Use pop() to remove by index and return the removed value, or remove() to delete the first matching value.

>>> ips.append("192.168.1.4")
>>> ips
['192.168.1.1', '192.168.1.2', '192.168.1.3', '192.168.1.4']
>>> ips.pop()
'192.168.1.4'
>>> ips.remove("192.168.1.2")
>>> ips
['192.168.1.1', '192.168.1.3']

The + operator joins lists. The len() function counts their items.

>>> routers = ["R1", "R2"]
>>> switches = ["S1", "S2"]
>>> devices = routers + switches
>>> devices
['R1', 'R2', 'S1', 'S2']
>>> len(devices)
4

A list can contain another list. This can keep two groups separate:

>>> router_ips = ["192.168.1.1", "192.168.1.2", "192.168.1.3"]
>>> switch_ips = ["172.16.1.1", "172.16.1.2", "172.16.1.3"]
>>> routers_switches = [router_ips, switch_ips]
>>> routers_switches
[['192.168.1.1', '192.168.1.2', '192.168.1.3'], ['172.16.1.1', '172.16.1.2', '172.16.1.3']]

min() and max() find the lowest and highest comparable items. split() is useful when one line of text contains values separated by commas.

>>> min([1, 2, 3, 4, 5, 6])
1
>>> max([1, 2, 3, 4, 5, 6])
6
>>> list("Router")
['R', 'o', 'u', 't', 'e', 'r']
>>> "R1,192.168.1.1,IOS XE".split(",")
['R1', '192.168.1.1', 'IOS XE']

4. Python Tuples

A tuple is ordered but fixed. You cannot add, remove, or replace an item in the tuple. Use it when the group should not change during the program.

>>> devices = ("R1", "R2", "SW1")
>>> devices[0]
'R1'
>>> devices[-1]
'SW1'
>>> devices.append("R3")
AttributeError: 'tuple' object has no attribute 'append'

The same applies to removal methods such as pop(): those methods are available on mutable lists, not tuples.

To represent a changed set, create a new tuple and assign it to the variable:

>>> devices = ("R1", "R2", "R3")
>>> devices
('R1', 'R2', 'R3')

The main benefit is clear intent: a tuple tells the reader that these ordered values should stay fixed.

5. Python Dictionaries

A dictionary stores a value behind a unique key. A key such as "site" is easier to understand than a numeric position.

>>> routers = {
...     "R1": "10.0.0.1",
...     "R2": "10.0.0.2",
...     "R3": "10.0.0.3"
... }
>>> routers["R1"]
'10.0.0.1'

A dictionary value can be text, a number, a list, or another dictionary:

>>> switches = {
...     "SW1": ["172.16.1.1", "3750"],
...     "SW2": ["172.16.1.2", "3850"]
... }
>>> switches["SW2"]
['172.16.1.2', '3850']

6. Dictionary Operations

Assign a value to an existing key to update it. Assign a value to a new key to add it. Use pop() or del to remove an entry.

>>> routers["R1"] = "10.0.0.10"
>>> routers["R4"] = "10.0.0.4"
>>> routers.pop("R2")
'10.0.0.2'
>>> "R1" in routers
True
>>> "R5" in routers
False

A value can itself be a dictionary. Nested dictionaries keep related details together for each device.

>>> devices = {
...     "R1": {
...         "ip": "10.0.0.1",
...         "model": "ISR4331",
...         "site": "HQ"
...     }
... }
>>> devices["R1"]["site"]
'HQ'

Real-world example: create a change target

target = {
    "name": "SW1",
    "ip": "192.0.2.20",
    "site": "Branch-01",
    "interfaces": ["GigabitEthernet1/0/1", "GigabitEthernet1/0/2"],
}

print(target["name"], target["site"], len(target["interfaces"]))

The output is SW1 Branch-01 2. The dictionary keeps the device facts together, while the list holds the interfaces included in the task.

7. Choosing the Right Collection

8. Conclusion

• Lists are ordered, mutable collections that use square brackets.
• Tuples are ordered, immutable collections that use parentheses.
• Dictionaries store values behind unique keys and use curly braces.
• Lists and tuples use indexes; dictionaries use keys.
• Nested dictionaries can model detailed network-device records.