api_method.py

from google.cloud import bigquery
import google.auth

def query():
    credentials, project = google.auth.default( scopes=[ "https://www.googleapis.com/auth/bigquery.readonly"] )

    client = bigquery.Client(credentials=credentials, project=project)
    query = "SELECT 1"
    results = client.query(query, api_method=bigquery.enums.QueryApiMethod.QUERY).result()
    for row in results:
        print(row)

def insert():
    # It should fail
    credentials, project = google.auth.default( scopes=[ "https://www.googleapis.com/auth/bigquery.readonly"] )

    # It should work
    # credentials, project = google.auth.default( scopes=[ "https://www.googleapis.com/auth/bigquery"] )

    client = bigquery.Client(credentials=credentials, project=project)
    query = "SELECT 1"
    results = client.query(query, api_method=bigquery.enums.QueryApiMethod.INSERT).result()
    for row in results:
        print(row)

query()
insert()

result.txt

(.venv) $ GOOGLE_APPLICATION_CREDENTIALS=${HOME}/Downloads/gsa-cred.json python script.py
Row((1,), {'f0_': 0})
Traceback (most recent call last):
...
google.api_core.exceptions.Forbidden: 403 POST https://bigquery.googleapis.com/bigquery/v2/projects/<my-project>/jobs?prettyPrint=false: Request had insufficient authentication scopes.