misc: mark strptime as a @stringfilter (#19576)

combo/public/templatetags/combo.py

@@ -22,6 +22,7 @@ from django import template
 from django.core.exceptions import PermissionDenied
 from django.template import RequestContext
 from django.template.base import TOKEN_BLOCK, TOKEN_VAR
+from django.template.defaultfilters import stringfilter
 from django.utils import dateparse
 
 from combo.data.models import Placeholder
@@ -149,6 +150,7 @@ def page_absolute_url(context, page):
     return context['request'].build_absolute_uri(page.get_online_url())
 
 @register.filter(name='strptime')
+@stringfilter
 def strptime(date_string, date_format):
     try:
         return datetime.datetime.strptime(date_string, date_format)

tests/test_public_templatetags.py

@@ -11,6 +11,7 @@ def test_strptime():
     t = Template('{% load combo %}{{ someday|strptime:"%Y-%m-%d"|date:"Y" }}')
     assert t.render(Context({'someday': '2015-04-15'})) == '2015'
     assert t.render(Context({'someday': 'foobar'})) == ''
+    assert t.render(Context({'someday': None})) == ''
 
 def test_parse_datetime():
     t = Template('{% load combo %}{{ someday|parse_datetime|date:"Y m d H i s T" }}')