CODEWITHSUNDEEP
pythonfor-loopboto3
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Reputation: 447

Python for loop. Extract specific value from AWS

I'm trying to get a for loop to work in boto3 and even though I have it working, it was hard to figure it out. At the moment I have:

  `spot_requests = ec2.describe_spot_instance_requests()
   for index in spot_requests['SpotInstanceRequests']:
        instanceID = index["InstanceId"]
        instanceState = index["State"]
        spotRequestID = index["SpotInstanceRequestId"]

    print(f'{instanceID} is {instanceState} and has a request ID of {spotRequestID}')`

which returns something like:

"I-1234556 IS disabled and has a request ID of sir-12344"

what I don't understand is why the index needs to be there after the = sign and why it errors if I just have:

instanceID = ["InstanceId"]

Also, I understand how dictionaries work, you reference the dictionary name and then in [square brackets] the key that you want to find the value for. However, when I try this (which is correct apparently)

    `describe_instance = ec2.describe_instances()
     for item2 in describe_instance['Reservations']:
        instance_state = item2['Instances'][0]["State"]["Name"]`

I don't understand what the [0] is doing as there is no key in the dictionary with 0 value. And what would I do if there was a nested dictionary in this? would it be something like this:

describe_instance = ec2.describe_instances()
 for item2 in describe_instance['Reservations']:
     instance_state = item2['Instances'][0]["State"]["Name"][0]["Nested value I want to find"]

thank you

Upvotes: 0

Views: 148

Answers (1)

isak
isak

Reputation: 140

what I don't understand is why the index needs to be there after the = sign and why it errors if I just have:

"index" is there because that is the dict that you want to get the specified value from.

I don't understand what the [0] is doing as there is no key in the dictionary with 0 value.

The [<number>] syntax indicates that you are trying to get a value from a a list, where the number indicates which index in the list you want to get. In you specific case the 'Instances' object in item2 is a list of dicts containing information about all the EC2 instances. Which is why you can use ['State']['Name'] to get the name of the state that the instance is currently in.

And what would I do if there was a nested dictionary in this? would it be something like this:

If the 'Name' field would contain a list of dicts (which wouldn't make sense) then you could do what you are suggesting in your last example.

Upvotes: 1

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