Extend EMPTY_VALUES for the form and|or model field

[Vladimir Prudnikov]

By default any values which is in validators.EMPTY_VALUES interpreted as an empty value. It would be great to be able to extend EMPTY_VALUES for the field by providing field argument empty_values which is a list of additional values interpreted as empty.

parent = forms.ModelChoiceField(...., empty_values=["null", "None"])

This is very useful for public API's. Here is an example of how external script can generate POST or GET data which will have different meaning in the Django's form:

>>> import urllib
>>> urllib.urlencode({"name":"Hello","parent":None})
'name=Hello&parent=None'

What do you think?

[Aymeric Augustin]

While this may be appropriate for your particular use case, it sounds like a anti-feature to me:

>>> import urllib
>>> urllib.urlencode({"name":"Hello","parent":"None"})       # my parent is actually called "None", anything wrong with that?
'name=Hello&parent=None'

If you need this logic in your app, you may implement it:

• for a specific field, in your (Model)Form's clean_<field> method
• for all fields of a model, in your (Model)Form's clean method (by iterating over all fields)
• for all fields of all models, in the clean method of a mixin class that you'll add to your (Model)Forms

[Vladimir Prudnikov]

clean_<field> method is not called if you pass "None" into UrlField or EmailField.
REmoving error messages from form.errors manually doens't seems a good solution to me...

>>> urllib.urlencode({"name":"Hello","parent":"None"})       # my parent is actually called "None", anything wrong with that?

If developer has defined string "None" as real None I don't see anything wrong with that.

I think this feature is quite similar anti-feature as validators attribute because the same way developer can raise an exception when string "None" has passed for parent, anything wrong with that? Well, may be, but in this case why validators is not anti-feature and empty_values is?
I think flexibility is the key.