Django 1.0 custom admin two fields shown as one

I needed a way to have two model fields to be shown/edited on one form field. And I came up with the following.

(CurrencyField (expense) shows and edits fields `value` and `currency` in the actual model)

from django.contrib import admin
from budget.models import Expense
from django import forms
from django.forms.util import ValidationError

class CurrencyField(forms.CharField):
   def clean(self, value):
       amount = 0
       currency = ''
       try:
           amount = float(value.split(" ")[0].strip())
       except (ValueError, TypeError), te:
           raise ValidationError('Amount is incorrect!')
      
       try:
           currency = value.split(" ")[1].strip().upper()
           if len(currency) != 3:
               raise TypeError('cur')
       except (ValueError, TypeError), te:
           raise ValidationError('Currency is incorrect! Should be three letter universal sign (e.g. EUR)')
      
       return (amount, currency)

class ExpenseForm(forms.ModelForm):
   expense = CurrencyField()
   def __init__(self, *args, **kwargs):
       super(ExpenseForm, self).__init__(*args, **kwargs)
       self.initial['expense'] = "%s %s" % (self.instance.value or '',
                                            self.instance.currency or '')
  
   def save(self, commit=True):
       self.instance.value, self.instance.currency = self.cleaned_data['expense']
       return super(ExpenseForm, self).save(commit)
  
   class Meta:
       model = Expense

# Note added:
# Expense is like this:
# class Expense(models.Model):
#     ...
#     value = models.FloatField(...)    # This contains the amount of currency, like 120.32
#     currency = models.CharField(...)  # Currency is e.g. 'USD', 'EUR' identifier of currency
#     ...

class ExpenseAdmin(admin.ModelAdmin):
   list_display = ('date', 'time', 'local_currency', 'in_euro', 'description', 'tags')
   ordering = ('date','time')
   form = ExpenseForm
   fields = ('expense', 'date', 'time', 'description', 'tags')
  
admin.site.register(Expense, ExpenseAdmin)