def select_participant()

in api/choice_algorithm.py [0:0]

• 21 lines of code
• 6 McCabe index (conditional complexity)

def select_participant(wheel, participant):
    """
    Register the selection of a participant by updating the weights of all participants for a given wheel
    :param wheel: Wheel dictionary:
    {
      "id": string ID of the wheel (DDB Hash Key),
      "name": string name of the wheel,
      "participant_count": number of participants in the wheel,
    }
    :param participant: Participant dictionary:
    {
      "id": string ID of the participant (DDB Hash Key),
      "name": string name of the participant,
      "url": Participant's URL,
      "wheel_id": string ID of the wheel the participant belongs to,
      "weight": participant's weight in the selection algorithm
    }
    :return: None
    """

    num_participants = 0
    total_weight = Decimal(0)
    for p in WheelParticipant.iter_query(KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
        num_participants = num_participants+1
        total_weight += p['weight']

    # Factor is the number by which all weights must be multiplied
    # so total weight will be equal to the number of participants.
    factor = Decimal(num_participants) / total_weight

    if num_participants > 1:
        weight_share = participant['weight'] / Decimal(num_participants - 1)
        with WheelParticipant.batch_writer() as batch:
            # Redistribute and normalize the weights.
            for p in WheelParticipant.iter_query(KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
                if p['id'] == participant['id']:
                    p['weight'] = 0
                else:
                    p['weight'] += Decimal(weight_share)
                    p['weight'] *= factor
                batch.put_item(Item=p)
    Wheel.update_item(
        Key={'id': wheel['id']},
        **to_update_kwargs({'participant_count': num_participants})
    )