how to start the code in BigQuery for python
from google.cloud import bigquery
# Create a "Client" object
client = bigquery.Client()
# Construct a reference to the "hacker_news" dataset
dataset_ref = client.dataset("data_set_name", project="project_name")
# API request - fetch the dataset
dataset = client.get_dataset(dataset_ref)
# Construct a reference to the "a_table" table
table_ref = dataset_ref.table("a_table")
# API request - fetch the table
table = client.get_table(table_ref)
# Preview the first five lines of the "comments" table
client.list_rows(table, max_results=5).to_dataframe()