def list_s3_keys_in_bucket(s3client,
                           bucket,
                           prefix=''):
    """
    Returns a list of the keys situated at the given prefix in the given bucket

    :s3client: boto3.session.Session.client that represents a connection with s3
    :bucket: string representing the s3 bucket's name
    :prefix: string representing the base filepath to search at in the s3 bucket, default: ''
    """
    keys = []
    response = s3client.list_objects(Bucket=bucket, Prefix=prefix)['Contents']
    for csv in response:
        keys.append(csv['Key'])

    return keys