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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 process_user(ctx, param, value):
 """Return a user if exists."""

    if value:
        if value.isdigit():
            user = User.query.get(str(value))
        else:
            user = User.query.filter(User.email == value).one_or_none()
        return user