pre-set values before model form saving

forms.py

from django import forms
from myapp.models import MyObject

class MyObjectForm(forms.ModelForm):
    class Meta:
        model = MyObject

    def save(self, commit=True):
        o = super(MyObjectForm, self).save(commit=False)
        # o.value = "pre-set value fi user"
        if commit:
            o.save()
        return o