[Answered ]-Django Form unexpected keyword argument

You have to store the extra argument before calling super and afterwards use the stored argument

class SelectionFournisseur(forms.Form):
    def __init__(self, *args, **kwargs):
        self._choixF = kwargs.pop('choixF', None)
        super().__init__(*args, **kwargs)
        self.fields['Fournisseur'].choices = self._choixF

Now your extra argument does not interfere with the super().__init__ call.