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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 _build_session(username, password, trans_label=None):
    '''
    Create a session to be used when connecting to iControl REST.
    '''

    bigip = requests.session()
    bigip.auth = (username, password)
    bigip.verify = False
    bigip.headers.update({'Content-Type': 'application/json'})

    if trans_label:
        #pull the trans id from the grain
        trans_id = __salt__['grains.get']('bigip_f5_trans:{label}'.format(label=trans_label))

        if trans_id:
            bigip.headers.update({'X-F5-REST-Coordination-Id': trans_id})
        else:
            bigip.headers.update({'X-F5-REST-Coordination-Id': None})

    return bigip