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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_mentions(status_dict, exclude=[]):
 """ Given a status dictionary, return all people mentioned in the toot, excluding those in the list passed in exclude. """

    # Canonicalise the exclusion dictionary by lowercasing all names and
    # removing leading @'s
    for i, user in enumerate(exclude):
        user = user.casefold()
        if user[0] == "@":
            user = user[1:]

        exclude[i] = user

    users = [user["username"] for user in status_dict["mentions"]
             if user["username"].casefold() not in exclude]
    return users