Django-Admin: CharField As TextArea

I have

class Cab(models.Model):
    name  = models.CharField( max_length=20 )
    descr = models.CharField( max_length=2000 )

class Cab_Admin(admin.ModelAdmin):
    ordering     = ('name',)
    list_display = ('name','descr', )
    # what to write here to make descr using TextArea?

admin.site.register( Cab, Cab_Admin )

how to assign TextArea widget to 'descr' field in admin interface?

upd:
In Admin interface only!

Good idea to use ModelForm.

You will have to create a forms.ModelForm that will describe how you want the descr field to be displayed, and then tell admin.ModelAdmin to use that form. For example:

from django import forms
class CabModelForm( forms.ModelForm ):
    descr = forms.CharField( widget=forms.Textarea )
    class Meta:
        model = Cab

class Cab_Admin( admin.ModelAdmin ):
    form = CabModelForm

The form attribute of admin.ModelAdmin is documented in the official Django documentation. Here is one place to look at.