Limit length of ListField in mongoengine

Could I limit the length of a ListField data in mongoengie without if condition?

I need something like this:

list = db.ListField(IntField(), max_length = 24)

in my document.

Or I have to check the length of my list when it's going to be update and don't update it if the length of my list greater than 24!

There is nothing like this built into the ListField, but you can make your custom ListField providing a max_length attribute:

class MyListField(ListField):
    def __init__(self, max_length=None,  **kwargs):
        self.max_length = max_length
        super(MyListField, self).__init__(**kwargs)

    def validate(self, value):
        super(MyListField, self).validate(value)

        if self.max_length is not None and len(value) > self.max_length:
            self.error('Too many items in the list')