Sets a step of 1 for the quantity field of InvoiceDetail

coin/billing/admin.py

@@ -6,6 +6,7 @@ from django.contrib import messages
 from django.http import HttpResponseRedirect
 from django.conf.urls import url
 from django.contrib.admin.utils import flatten_fieldsets
+from django import forms
 
 from coin.filtering_queryset import LimitedAdminInlineMixin
 from coin.billing.models import Invoice, InvoiceDetail, Payment, PaymentAllocation
@@ -14,11 +15,22 @@ from django.core.urlresolvers import reverse
 import autocomplete_light
 
 
+class InvoiceDetailInlineForm(forms.ModelForm):
+    class Meta:
+        model = InvoiceDetail
+        fields = (
+            'label', 'amount', 'quantity', 'tax',
+            'offersubscription', 'period_from', 'period_to'
+        )
+        widgets = {'quantity': forms.NumberInput(attrs={'step': 1})}
+
+
 class InvoiceDetailInline(LimitedAdminInlineMixin, admin.StackedInline):
     model = InvoiceDetail
     extra = 0
     fields = (('label', 'amount', 'quantity', 'tax'),
               ('offersubscription', 'period_from', 'period_to'))
+    form = InvoiceDetailInlineForm
 
     def get_filters(self, obj):
         """