Code Snippet for Using Impersonation

Spanner 

from google.cloud import spanner

import google.auth

from google.auth import impersonated_credentials

credentials ,project = google.auth.default() #get default credentials and project

target_credentials = impersonated_credentials.Credentials(source_credentials=credentials,

 target_principals = impersonate_sa_to, #give sa to which you want to impersonate 

target_scopes=["https://www.googleapis.com/auth/cloud-platform"]

)

spanner_client=spanner.Client(credentials=target_credentials)

instance = spanner_client.instance(instance_id)

database=instance.database(database_id)