forms.py

from django import forms
class NewReportTypeForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        self.report_belongs_to_lab = kwargs.pop('report_belongs_to_lab', None)
        super(NewReportTypeForm, self).__init__(*args, **kwargs)

    def save(self, commit=True):
        instance = super(NewReportTypeForm, self).save(commit=False)
        if self.report_belongs_to_lab:
            instance.report_belongs_to_lab = self.report_belongs_to_lab
        return instance.save()
 
    class Meta:
        model = ReportTypes
        exclude = ('report_belongs_to_lab') #Dont include it in the form !