How do I iterate through 2 nested for loops in Python?

Question

I have a script that pulls server info from GCP that works fine:

import googleapiclient.discovery
compute = googleapiclient.discovery.build('compute', 'v1')
project_id = 'company-dev'
zone = 'us-east1-d'
def list_instances(compute,project_id,date):
    zone = 'us-east1-d'
    delete_from_collection(date)
    result = compute.instances().list(project=project_id, zone=zone).execute()
    items = result['items']
    for item in items:
        instance_id = item['id']
        name = item['name']
        timestamp = item['creationTimestamp']
        private_ip = item['networkInterfaces'][0]['networkIP']
        #network = item['networkInterfaces'][0]['network']
        instance_dict = {'Instance ID': instance_id, 'Name': name,'Network Interfaces': private_ip,'Timestamp': timestamp,}
        #print(instance_dict)
        insert_coll(instance_dict,date)

But I need to alter this function so that it also loops through a list of zones. And when I add the zones list and another for loop for the zones list it loses sight of a variable called items = result['items'] that works in the previous version.

This function with the added for loop:

def list_instances(compute,project_id,date):
    delete_from_collection(date)
    zones = ['us-east1-b','us-east1-c','us-east1-d','us-east4-c','us-east4-b','us-east4-a']
    for zone in zones:
        result = compute.instances().list(project=project_id, zone=zone).execute()
        items = result['items']
        for item in items:
            instance_id = item['id']
            name = item['name']
            timestamp = item['creationTimestamp']
            private_ip = item['networkInterfaces'][0]['networkIP']
            #network = item['networkInterfaces'][0]['network']
            instance_dict = {'Instance ID': instance_id, 'Name': name,'Network Interfaces': private_ip,'Timestamp': timestamp,}
            #print(instance_dict)
            insert_coll(instance_dict,date)

Produces the following error:

Traceback (most recent call last):
  File "gcp_list_instances.py", line 379, in <module>
    main()
  File "gcp_list_instances.py", line 370, in main
    list_instances(compute,project_id,date)
  File "gcp_list_instances.py", line 151, in list_instances
    items = result['items']
KeyError: 'items'

Why does the inner for loop lose track of the items = result['items'] variable? And how can I get the inner for loop to recognize that variable?

Answer 1

As I mentioned in comments, earlier, you can just provide a default value, so you don't get an exception. And if the empty list is your default, you can still iterate over it. The trick here is "nothing happens" so this code gracefully skips over those errors:

for item in result.get('items', []):
    insert_coll_stuff(item)

docs: https://docs.python.org/3/library/stdtypes.html?highlight=get#dict.get
example: https://stackoverflow.com/a/11041421/1766544

Answer 2

The problem was that there were no servers in some of the zones. So the items variable wouldn't exist in those zones.

Wrapping the code that creates the result variable in a try block solved the problem. This is the final version of the function:

def list_instances(compute,project_id,date):
    delete_from_collection(date)
    items = []
    zones = ['us-east1-b','us-east1-c','us-east1-d','us-east4-c','us-east4-b','us-east4-a','us-central1-c','us-central1-a','us-central1-f','us-central1-b','us-west1-b','us-west1-c','us-west1-a','europe-west4-a','europe-west4-b','europe-west4-c','europe-west1-b','europe-west1-d','europe-west1-c','europe-central2-a','europe-central2-b','europe-central2-c','europe-north1-a','europe-north1-b','europe-north1-c','europe-west6-a','europe-west6-b','europe-west6-c','northamerica-northeast1-a','northamerica-northeast1-b','northamerica-northeast1-c','us-west2-a','us-west2-b','us-west2-c','us-west3-a','us-west3-b','us-west3-c','us-west4-a','us-west4-b','us-west4-c']
    for zone in zones:
        try:
            result = compute.instances().list(project=project_id, zone=zone).execute()
            items = result['items']
        except Exception as e:
            pass
        if items:
            for item in items:
                instance_id = item['id']
                name = item['name']
                timestamp = item['creationTimestamp']
                private_ip = item['networkInterfaces'][0]['networkIP']
                instance_dict = {'Instance ID': instance_id, 'Name': name,'Network Interfaces': private_ip,'Timestamp': timestamp,}
                insert_coll(instance_dict,date)