from typing import List


def participant_de_dupe(participants) -> List:
    """ Take a list of participants and return a deduped list (based on email). """
    checked_emails = []
    deduped = []
    for participant in participants:
        email = participant.email
        if email not in checked_emails:
            checked_emails.append(email)
            deduped.append(participant)

    return deduped