Determine Django form field clean order

Django provides some excellent out-of-the-box form validation/processing mechanisms. These include casual forms, model based forms, and formsets. One of their features is the ease of implementing data validation procedures. According to the documentation, the validation process includes executing the following methods in the presented order:

1. to_python (field)
2. validate (field)
3. run_validators (field)
4. clean (field)
5. clean_<fieldname> (form)
6. clean (form)

Since there is usually no need to extend form fields, let's focus on the form-side validation. Let's suppose you have the following forms:

class MyBaseForm(forms.Form):
    base_field1 = forms.CharField()
    base_field2 = forms.CharField()

    def clean_base_field1(self):
        #(...)
        return self.cleaned_data['base_field1']
       
    def clean_base_field2(self):
        #(...)
        return self.cleaned_data['base_field2']

class MyForm(MyBaseForm):
    field1 = forms.CharField()

    def clean_field1(self):
        #(...)
        return self.cleaned_data['field1']

All methods implemented in this example refer to step 5: clean_<fieldname>. So what would be the execution order if we try validating MyForm? Django manual states:

"These methods are run in the order given above, one field at a time. That is, for each field in the form (in the order they are declared in the form definition), the Field.clean() method (or its override) is run, then clean_<fieldname>(). Finally, once those two methods are run for every field, the Form.clean() method, or its override, is executed."

According to this statement, the expected order would be: clean_base_field1, clean_base_field2, field1. What if we don't like this order, should we rearrange the form definition? No such thing! There is a way change this order in a more elegant way. We may use fields.keyOrder to achieve it:

class MyForm(MyBaseForm):
    field1 = forms.CharField()

    def clean_field1(self):
        #(...)
        return self.cleaned_data['field1']

    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.fields.keyOrder = ['base_field1', 'field1', 'base_field2']

You don't need to extend a form to use this. You may also specify a partial order (if there are to many fields to be named explicitly) by putting only a few field names in the array and extending it by a list comprehension generated from the remaining self.fields.keys(). 

Cheers! 

~KR