Let me share with you this documentation page, where there is a detailed explanation on how to build a script such as the one you shared, and what does each line of code mean. It is extracted from the documentation of ML Engine, not IAM, but it is using the same Python Google API Client Libary, so just ignore the references to ML and the rest will be useful for you.
In any case, here it is a commented version of your code, so that you understand it better:
# Imports for the Client API Libraries and the key management
import os
from googleapiclient import discovery
from gcp import get_key
# Look for an environment variable containing the credentials for Google Cloud Platform
os.environ["GOOGLE_APPLICATION_CREDENTIALS"] = get_key()
# Build a Python representation of the REST API
service = discovery.build('iam', 'v1')
# Define the Project ID of your project
project_id = 'projects/<google cloud project>'
"""Until this point, the code is general to any API
From this point on, it is specific to the IAM API"""
# Create the request using the appropriate 'serviceAccounts' API
# You can substitute serviceAccounts by any other available API
request = service.projects().serviceAccounts().list(name=project_id)
# Execute the request that was built in the previous step
response = request.execute()
# Process the data from the response obtained with the request execution
accounts = response['accounts']
for account in accounts:
print(account['email'])
Once you understand the first part of the code, the last lines are specific to the API you are using, which in this case is the Google IAM API. In this link, you can find detailed information on the methods available and what they do.
Then, you can follow the Python API Client Library documentation that you shared in order to see how to call the methods. For instance, in the code you shared, the method used depends on service, which is the Python representation of the API, and then goes down the tree of methods in the last link as in projects(), then serviceAccounts() and finally the specificlist() method, which ends up in request = service.projects().serviceAccounts().list(name=project_id).
Finally, just in case you are interested in the other available APIs, please refer to this page for more information.
I hope the comments I made on your code were of help, and that the documentation shared makes it easier for you to understand how a code like that one could be scripted.
