Remove dependency on django.utils.six

This is done to prepare for upgrade to Django 3.x, which drops six.

Refs #1649

judge/contest_format/base.py

@@ -1,7 +1,5 @@
 from abc import ABCMeta, abstractmethod, abstractproperty
 
-from django.utils import six
-
 
 class abstractclassmethod(classmethod):
     __isabstractmethod__ = True
@@ -11,7 +9,7 @@ def __init__(self, callable):
         super(abstractclassmethod, self).__init__(callable)
 
 
-class BaseContestFormat(six.with_metaclass(ABCMeta)):
+class BaseContestFormat(metaclass=ABCMeta):
     @abstractmethod
     def __init__(self, contest, config):
         self.config = config

judge/contest_format/registry.py

@@ -1,5 +1,3 @@
-from django.utils import six
-
 formats = {}
 
 
@@ -13,4 +11,4 @@ def register_class(contest_format_class):
 
 
 def choices():
-    return [(key, value.name) for key, value in sorted(six.iteritems(formats))]
+    return [(key, value.name) for key, value in sorted(formats.items())]

judge/jinja2/rating.py

@@ -1,5 +1,3 @@
-from django.utils import six
-
 from judge.ratings import rating_class, rating_name, rating_progress
 from . import registry
 
@@ -8,7 +6,7 @@ def _get_rating_value(func, obj):
     if obj is None:
         return None
 
-    if isinstance(obj, six.integer_types):
+    if isinstance(obj, int):
         return func(obj)
     else:
         return func(obj.rating)

judge/user_translations.py

@@ -1,5 +1,4 @@
 from django.conf import settings
-from django.utils import six
 from django.utils.safestring import SafeData, mark_safe
 
 if settings.USE_I18N:
@@ -25,7 +24,7 @@ def do_translate(message, translation_function):
         else:
             translation_object = translation(get_language())
             result = getattr(translation_object, translation_function)(eol_message)
-            if not isinstance(result, six.text_type):
+            if not isinstance(result, str):
                 result = result.decode('utf-8')
 
         if isinstance(message, SafeData):

judge/utils/pwned.py

@@ -40,7 +40,6 @@
 from django.conf import settings
 from django.contrib.auth.password_validation import CommonPasswordValidator
 from django.core.exceptions import ValidationError
-from django.utils.six import string_types
 from django.utils.translation import gettext as _, ungettext
 
 from judge.utils.unicode import utf8bytes
@@ -83,7 +82,7 @@ def pwned_password(password):
     """
     Checks a password against the Pwned Passwords database.
     """
-    if not isinstance(password, string_types):
+    if not isinstance(password, str):
         raise TypeError('Password values to check must be strings.')
     password_hash = hashlib.sha1(utf8bytes(password)).hexdigest().upper()
     prefix, suffix = password_hash[:5], password_hash[5:]
@@ -106,7 +105,7 @@ def __init__(self, error_message=None, help_message=None):
         error_message = error_message or self.DEFAULT_PWNED_MESSAGE
 
         # If there is no plural, use the same message for both forms.
-        if isinstance(error_message, string_types):
+        if isinstance(error_message, str):
             singular, plural = error_message, error_message
         else:
             singular, plural = error_message

judge/utils/raw_sql.py

@@ -5,7 +5,6 @@
 from django.db.models.expressions import RawSQL
 from django.db.models.sql.constants import INNER, LOUTER
 from django.db.models.sql.datastructures import Join
-from django.utils import six
 
 from judge.utils.cachedict import CacheDict
 
@@ -66,7 +65,7 @@ def RawSQLColumn(model, field=None):
     if isinstance(model, Field):
         field = model
         model = field.model
-    if isinstance(field, six.string_types):
+    if isinstance(field, str):
         field = model._meta.get_field(field)
     return RawSQL('%s.%s' % (model._meta.db_table, field.get_attname_column()[1]), ())
 

judge/views/status.py

@@ -2,7 +2,6 @@
 from functools import partial
 
 from django.shortcuts import render
-from django.utils import six
 from django.utils.translation import gettext as _
 from packaging import version
 
@@ -66,12 +65,12 @@ def version_matrix(request):
     for runtime in RuntimeVersion.objects.filter(judge__online=True).order_by('priority'):
         matrix[runtime.judge_id][runtime.language_id].append(runtime)
 
-    for judge, data in six.iteritems(matrix):
+    for judge, data in matrix.items():
         name_tuple = judges[judge].rpartition('.')
         groups[name_tuple[0] or name_tuple[-1]].append((judges[judge], data))
 
     matrix = {}
-    for group, data in six.iteritems(groups):
+    for group, data in groups.items():
         if len(data) == 1:
             judge, data = data[0]
             matrix[judge] = data
@@ -94,14 +93,14 @@ def version_matrix(request):
             if ds[i] != rep:
                 matrix[j] = x
 
-    for data in six.itervalues(matrix):
-        for language, versions in six.iteritems(data):
+    for data in matrix.values():
+        for language, versions in data.items():
             versions.versions = [version.parse(runtime.version) for runtime in versions]
             if versions.versions > latest[language]:
                 latest[language] = versions.versions
 
-    for data in six.itervalues(matrix):
-        for language, versions in six.iteritems(data):
+    for data in matrix.values():
+        for language, versions in data.items():
             versions.is_latest = versions.versions == latest[language]
 
     languages = sorted(languages, key=lambda lang: version.parse(lang.name))