Setting GOOGLE_APPLICATION_CREDENTIALS for BigQuery Python CLI

I'm trying to connect to Google BigQuery through the BigQuery API, using Python.

I'm following this page here:
https://cloud.google.com/bigquery/bigquery-api-quickstart

My code is as follows:

import os
import argparse

from apiclient.discovery import build
from apiclient.errors import HttpError
from oauth2client.client import GoogleCredentials

GOOGLE_APPLICATION_CREDENTIALS = './google-creds.json'

def main(project_id):
    # Grab the application's default credentials from the environment.
    credentials = GoogleCredentials.get_application_default()
    print(credentials)
    # Construct the service object for interacting with the BigQuery API.
    bigquery_service = build('bigquery', 'v2', credentials=credentials)

    try:
        query_request = bigquery_service.jobs()
        query_data = {
            'query': (
                'SELECT TOP(corpus, 10) as title, '
                'COUNT(*) as unique_words '
                'FROM [publicdata:samples.shakespeare];')
        }

        query_response = query_request.query(
            projectId=project_id,
            body=query_data).execute()

        print('Query Results:')
        for row in query_response['rows']:
            print('\t'.join(field['v'] for field in row['f']))

    except HttpError as err:
        print('Error: {}'.format(err.content))
        raise err


if __name__ == '__main__':
    parser = argparse.ArgumentParser(
        description=__doc__,
        formatter_class=argparse.RawDescriptionHelpFormatter)
    parser.add_argument('project_id', help='Your Google Cloud Project ID.')

    args = parser.parse_args()

    main(args.project_id)

However, when I run this code through the terminal, I get the following error:

oauth2client.client.ApplicationDefaultCredentialsError: The Application Default Credentials are not available. They are available if running in Google Compute Engine. Otherwise, the environment variable GOOGLE_APPLICATION_CREDENTIALS must be defined pointing to a file defining the credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.

As you can see in the code, I've tried to set the GOOGLE_APPLICATION_CREDENTIALS as per the link in the error. However, the error persists. Does anyone know what the issue is?

First - Thanks for the code - this provided to be very useful. I would also suggest adding setting the environmental variable directly in your code - as not to set it for every environment you work on. you can use the following code:

import os
os.environ["GOOGLE_APPLICATION_CREDENTIALS"] = "path_to_your_.json_credential_file"

I found this useful when switching between different projects that require different credentials.