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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_bq_service(credentials=None, service_url=None):
 """Construct an authorized BigQuery service object."""


    assert credentials, 'Must provide ServiceAccountCredentials'

    http = credentials.authorize(Http())
    service = build(
        'bigquery',
        'v2',
        http=http,
        discoveryServiceUrl=service_url,
        cache_discovery=False
    )

    return service