How can I limit MultipleChoiceField's showing Items?

I have a MultipleChoiceField. I need to assign a integer value which provides that MultipleChoiceField shows only this number of element on the website? How can I do that?

Another question is where can I find any documentation whi开发者_高级运维ch contains answers of these question? I need a document like QT Asistant.

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You can modify the choices of any choice field on init.

Consider this

class BookForm(forms.Form):
    book = forms.ModelChoiceField(queryset=Book.objects.all())
    user = forms.EmailField()

    def __init__(self, author=None, *args, **kwargs):
        super(CheckoutForm, self).__init__(*args, **kwargs)
        if author:
            self.fields['book'].queryset = Book.objects.filter(author__icontains=author)

In this example, you could call BookForm() like normal, or you could call BookForm(author="Tolkien")

That's how you would modify ModelChoices on the fly, you could see, it's the same process to modify normal choices on the fly as well, just pass an iterable (usually of 2-tuples)