Nested Python lists and dicts

Looping and direct access

When working with JSON based REST APIs, it is common to receive responses with nested data structures in various combinations.

After converting JSON to a Python data structure we can easily iterate through it thanks to the built-in flexibility of the for-loop in Python, or they can be accessed directly with list indices or key references.

The following examples serve as a basic reference to working with nested data structures using lists and dictionaries.

In the examples below you can see various methods on accessing data with the following nested formats:

list
dict
list of lists
list of dicts
dict of lists
dict of dicts

With each of those data structures you will see how to:

loop through keys and/or values
reference elements directly without looping
extract subsections of a list
simple error handling for invalid dict key

Not all of the examples are perfect for every situation, so it's up to you to evaluate what method makes most sense in your case.

List

Example list

network_fundamentals_list = [
  "vlan",
  "mac-address",
  "vrf",
  "ip-address"
]

Loop through a list

for network_concept in network_fundamentals_list:
  print(network_concept)

Output

vlan
mac-address
vrf
ip-address

4 ways of direct list access

Pick the most simplest one suitable for your use-case:

print(network_fundamentals_list[2])
print(network_fundamentals_list[-1])
print(network_fundamentals_list[1:2])
print(network_fundamentals_list[2:])

Output

vrf
ip-address
['mac-address']
['vrf', 'ip-address']

Dictionary

Example dictionary

network_fundamentals_dict = {
  "vlan": "broadcast domain",
  "mac-address": "physical address",
  "vrf": "routing instance",
  "ip-address": "logical address"
}

Loop through dictionary keys

for network_concept in network_fundamentals_dict.keys():
  print(network_concept)

Output

vlan
mac-address
vrf
ip-address

Loop through dictionary values

for description in network_fundamentals_dict.values():
  print(description)

Output

broadcast domain
physical address
routing instance
logical address

Loop through dictionary entries (items)

for network_concept, description in network_fundamentals_dict.items():
  print(network_concept + " is a " + description)

Output

vlan is a broadcast domain
mac-address is a physical address
vrf is a routing instance
ip-address is a logical address

4 ways of direct dict access

Pick the most simplest one suitable for your use-case

print(network_fundamentals_dict["vlan"])
print(network_fundamentals_dict.get("ipv6-anycast", "NO SUCH ELEMENT!"))
print(list(network_fundamentals_dict.values())[1])
print(list(network_fundamentals_dict.keys())[2])

Output

broadcast domain
NO SUCH ELEMENT!
physical address
vrf

List of lists

Example list of lists

network_fundamentals_outer_list = [
  [
    "vlan",
    "mac-address"
  ],
  [
    "vrf",
    "ip-address"
  ]
]

Loop through a list of lists

for network_fundamentals_inner_list in network_fundamentals_outer_list:
  for network_concept in network_fundamentals_inner_list:
    print(network_concept)

Output

vlan
mac-address
vrf
ip-address

4 ways of direct access with lists of lists

Pick the most simplest one suitable for your use-case:

print(network_fundamentals_outer_list[0][0])
print(network_fundamentals_outer_list[0][1])
print(network_fundamentals_outer_list[1])
print(network_fundamentals_outer_list[-1][-1])

Output

vlan
mac-address
['vrf', 'ip-address']
ip-address

List of dictionaries

Example list of dictionaries

network_fundamentals_list_of_dicts = [
  {
    "vlan": "broadcast domain",
    "mac-address": "physical address"
  },
  {
    "vrf": "routing instance",
    "ip-address": "logical address"
  }
]

Loop through keys of a list of dictionaries

for network_fundamentals_inner_dict in network_fundamentals_list_of_dicts:
  for network_concept in network_fundamentals_inner_dict.keys():
    print(network_concept)

Output

vlan
mac-address
vrf
ip-address

Loop through values of a list of dictionaries

for network_fundamentals_inner_dict in network_fundamentals_list_of_dicts:
  for description in network_fundamentals_inner_dict.values():
    print(description)

Output

broadcast domain
physical address
routing instance
logical address

Loop through entries of a list of dictionaries

for network_fundamentals_inner_dict in network_fundamentals_list_of_dicts:
  for network_concept, description in network_fundamentals_inner_dict.items():
    print(network_concept + " is a " + description)

Output

vlan is a broadcast domain
mac-address is a physical address
vrf is a routing instance
ip-address is a logical address

4 ways of direct access of list of dictionaries

Pick the simplest one suitable for your use-case:

print(network_fundamentals_list_of_dicts[0]["vlan"])
print(list(network_fundamentals_list_of_dicts[0].values())[1])
print(list(network_fundamentals_list_of_dicts[1].keys())[0])
print(network_fundamentals_list_of_dicts[-1]["ip-address"])

Output

broadcast domain
physical address
vrf
logical address

Dictionary of lists

Example Dictionary of lists

network_fundamentals_outer_dict = {
  "layer-2": [
    "vlan",
    "mac-address"
  ],
  "layer-3": [
    "vrf",
    "ip-address"
  ]
}

Loop through a dictionary of lists

for osi_model_layer, network_fundamentals_inner_list in network_fundamentals_outer_dict.items():
  for network_concept in network_fundamentals_inner_list:
    print(network_concept + " belongs to ISO model " + osi_model_layer)

Output

vlan belongs to ISO model layer-2
mac-address belongs to ISO model layer-2
vrf belongs to ISO model layer-3
ip-address belongs to ISO model layer-3

4 ways of direct access a dictionary of lists

Pick the simplest one suitable for your use-case:

print(network_fundamentals_outer_dict["layer-2"][0])
print(network_fundamentals_outer_dict["layer-3"][-1])
print(list(network_fundamentals_outer_dict.values())[0][1])
print(list(network_fundamentals_outer_dict.keys())[1])

Output

vlan
ip-address
mac-address
layer-3

Dictionary of dictionaries

Example ictionary of dictionariesd

network_fundamentals_outer_dict = {
  "layer-2": {
    "vlan": "broadcast domain",
    "mac-address": "physical address"
  },
  "layer-3": {
    "vrf": "routing instance",
    "ip-address": "logical address"
  }
}

Loop through a dictionary of dictionaries

for osi_model_layer, network_fundamentals_inner_dict in network_fundamentals_outer_dict.items():
  for network_concept, description in network_fundamentals_inner_dict.items():
    print(network_concept + " is a " + description + " and belongs to ISO model " + osi_model_layer)

Output

vlan is a broadcast domain and belongs to ISO model layer-2
mac-address is a physical address and belongs to ISO model layer-2
vrf is a routing instance and belongs to ISO model layer-3
ip-address is a logical address and belongs to ISO model layer-3

4 ways of direct access of a dictionary of dictionaries

Pick the simplest one suitable for your use-case:

print(network_fundamentals_outer_dict["layer-2"]["mac-address"])
print(list(network_fundamentals_outer_dict.values())[0]["vlan"])
print(list(network_fundamentals_outer_dict["layer-3"].keys())[0])
print(list(network_fundamentals_outer_dict.keys())[1])

Output

physical address
broadcast domain
vrf
layer-3