Create a BigQuery client with a service account key file

bigquery_client_from_service_account_file.py

from google.cloud import bigquery
from google.oauth2 import service_account

# TODO(developer): Set key_path to the path to the service account key
#                  file.
# key_path = "path/to/service_account.json"

credentials = service_account.Credentials.from_service_account_file(
    key_path,
    scopes=["https://www.googleapis.com/auth/cloud-platform"],
)

# Alternatively, use service_account.Credentials.from_service_account_info()
# to set credentials directly via a json object rather than set a filepath
# TODO(developer): Set key_json to the content of the service account key file.
# credentials = service_account.Credentials.from_service_account_info(key_json)

client = bigquery.Client(
    credentials=credentials,
    project=credentials.project_id,
)