Python lists and dictionaries indexing - python-3.x

Question

In the AWS API documentation it wants me to call a function in the boto3 module like this:
response = client.put_metric_data(
Namespace='string',
MetricData=[
{
'MetricName': 'string',
'Dimensions': [
{
'Name': 'string',
'Value': 'string'
},
],
'Timestamp': datetime(2015, 1, 1),
'Value': 123.0,
'StatisticValues': {
'SampleCount': 123.0,
'Sum': 123.0,
'Minimum': 123.0,
'Maximum': 123.0
},
'Values': [
123.0,
],
'Counts': [
123.0,
],
'Unit': 'Seconds'|'Microseconds'|'Milliseconds'|'Bytes'|'Kilobytes'|'Megabytes'|'Gigabytes'|'Terabytes'|'Bits'|'Kilobits'|'Megabits'|'Gigabits'|'Terabits'|'Percent'|'Count'|'Bytes/Second'|'Kilobytes/Second'|'Megabytes/Second'|'Gigabytes/Second'|'Terabytes/Second'|'Bits/Second'|'Kilobits/Second'|'Megabits/Second'|'Gigabits/Second'|'Terabits/Second'|'Count/Second'|'None',
'StorageResolution': 123
},
]
)
So, I set a variable using the same format:
cw_metric = [
{
'MetricName': '',
'Dimensions': [
{
'Name': 'Protocol',
'Value': 'SSH'
},
],
'Timestamp': '',
'Value': 0,
'StatisticValues': {
'SampleCount': 1,
'Sum': 0,
'Minimum': 0,
'Maximum': 0
}
}
]
To my untrained eye, this looks simply like json and I am able to use json.dumps(cw_metric) to get a JSON formatted string output that looks, well, exactly the same.
But, apparently, in Python, when I use brackets I am creating a list and when I use curly brackets I am creating a dict. So what did I create above? A list of dicts or in the case of Dimensions a list of dicts with a list of dicts? Can someone help me to understand that?
And finally, now that I have created the cw_metric variable I want to update some of the values inside of it. I've tried several combinations. I want to do something like this:
cw_metric['StatisticValues']['SampleCount']=2
I am of course told that I can't use a str as an index on a list.
So, I try something like this:
cw_metric[4][0]=2
or
cw_metric[4]['SampleCount']=2
It all just ends up in errors.
I found that this works:
cw_metric[0]['StatisticValues']['SampleCount']=2
But, that just seems stupid. Is this the proper way to handle this?

Answer 1

cw_metric is a list of one dictionary. Thus, cw_metric[0] is that dictionary. cw_metric[0]['Dimensions'] is a list of one dictionary as well. cw_metric[0]['StatisticValues'] is just a dictionary. One of its elements is, for example, cw_metric[0]['StatisticValues']['SampleCount'] == 1.