Fixed #28860 -- Removed unnecessary len() calls.

django/contrib/admin/tests.py

@@ -158,7 +158,7 @@ class AdminSeleniumTestCase(SeleniumTestCase, StaticLiveServerTestCase):
             # to be the case.
             with self.disable_implicit_wait():
                 self.wait_until(
-                    lambda driver: len(driver.find_elements_by_css_selector(options_selector)) == 0
+                    lambda driver: not driver.find_elements_by_css_selector(options_selector)
                 )
 
     def assertSelectOptions(self, selector, values):

django/contrib/contenttypes/admin.py

@@ -25,7 +25,7 @@ class GenericInlineModelAdminChecks(InlineModelAdminChecks):
             f for f in obj.model._meta.private_fields
             if isinstance(f, GenericForeignKey)
         ]
-        if len(gfks) == 0:
+        if not gfks:
             return [
                 checks.Error(
                     "'%s.%s' has no GenericForeignKey." % (

django/contrib/flatpages/templatetags/flatpages.py

@@ -74,8 +74,7 @@ def get_flatpages(parser, token):
                       "['url_starts_with'] [for user] as context_name" %
                       {'tag_name': bits[0]})
     # Must have at 3-6 bits in the tag
-    if len(bits) >= 3 and len(bits) <= 6:
+    if 3 <= len(bits) <= 6:
-
         # If there's an even number of bits, there's no prefix
         if len(bits) % 2 == 0:
             prefix = bits[1]

django/contrib/gis/geoip2/resources.py

@@ -9,7 +9,7 @@ def City(response):
         'latitude': response.location.latitude,
         'longitude': response.location.longitude,
         'postal_code': response.postal.code,
-        'region': response.subdivisions[0].iso_code if len(response.subdivisions) else None,
+        'region': response.subdivisions[0].iso_code if response.subdivisions else None,
         'time_zone': response.location.time_zone,
     }
 

django/contrib/gis/geos/polygon.py

@@ -37,7 +37,7 @@ class Polygon(GEOSGeometry):
 
         # If initialized as Polygon(shell, (LinearRing, LinearRing)) [for backward-compatibility]
         if n_holes == 1 and isinstance(init_holes[0], (tuple, list)):
-            if len(init_holes[0]) == 0:
+            if not init_holes[0]:
                 init_holes = ()
                 n_holes = 0
             elif isinstance(init_holes[0][0], LinearRing):

django/core/management/__init__.py

@@ -351,7 +351,7 @@ class ManagementUtility:
         if subcommand == 'help':
             if '--commands' in args:
                 sys.stdout.write(self.main_help_text(commands_only=True) + '\n')
-            elif len(options.args) < 1:
+            elif not options.args:
                 sys.stdout.write(self.main_help_text() + '\n')
             else:
                 self.fetch_command(options.args[0]).print_help(self.prog_name, options.args[0])

django/core/management/commands/createcachetable.py

@@ -33,7 +33,7 @@ class Command(BaseCommand):
         db = options['database']
         self.verbosity = options['verbosity']
         dry_run = options['dry_run']
-        if len(tablenames):
+        if tablenames:
             # Legacy behavior, tablename specified as argument
             for tablename in tablenames:
                 self.create_table(db, tablename, dry_run)

django/core/management/commands/dumpdata.py

@@ -84,7 +84,7 @@ class Command(BaseCommand):
 
         excluded_models, excluded_apps = parse_apps_and_model_labels(excludes)
 
-        if len(app_labels) == 0:
+        if not app_labels:
             if primary_keys:
                 raise CommandError("You can only use --pks option with one model")
             app_list = OrderedDict.fromkeys(

django/core/management/commands/makemigrations.py

@@ -162,9 +162,10 @@ class Command(BaseCommand):
         if not changes:
             # No changes? Tell them.
             if self.verbosity >= 1:
+                if app_labels:
                     if len(app_labels) == 1:
                         self.stdout.write("No changes detected in app '%s'" % app_labels.pop())
-                elif len(app_labels) > 1:
+                    else:
                         self.stdout.write("No changes detected in apps '%s'" % ("', '".join(app_labels)))
                 else:
                     self.stdout.write("No changes detected")

django/db/backends/oracle/base.py

@@ -476,7 +476,7 @@ class FormatStylePlaceholderCursor:
             # Handle params as dict
             args = {k: ":%s" % k for k in params}
             query = query % args
-        elif unify_by_values and len(params) > 0:
+        elif unify_by_values and params:
             # Handle params as a dict with unified query parameters by their
             # values. It can be used only in single query execute() because
             # executemany() shares the formatted query with each of the params

django/db/backends/postgresql/operations.py

@@ -132,7 +132,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         for sequence_info in sequences:
             table_name = sequence_info['table']
             column_name = sequence_info['column']
-            if not (column_name and len(column_name) > 0):
+            if not column_name:
                 # This will be the case if it's an m2m using an autogenerated
                 # intermediate table (see BaseDatabaseIntrospection.sequence_list)
                 column_name = 'id'

django/db/migrations/autodetector.py

@@ -1219,7 +1219,7 @@ class MigrationAutodetector:
                 return "%s_%s" % (ops[0].model_name_lower, ops[0].name_lower)
             elif isinstance(ops[0], operations.RemoveField):
                 return "remove_%s_%s" % (ops[0].model_name_lower, ops[0].name_lower)
-        elif len(ops) > 1:
+        elif ops:
             if all(isinstance(o, operations.CreateModel) for o in ops):
                 return "_".join(sorted(o.name_lower for o in ops))
         return "auto_%s" % get_migration_name_timestamp()

django/db/migrations/graph.py

@@ -360,7 +360,7 @@ class MigrationGraph:
         """
         if nodes is None:
             nodes = list(self.leaf_nodes())
-        if len(nodes) == 0:
+        if not nodes:
             return ProjectState()
         if not isinstance(nodes[0], tuple):
             nodes = [nodes]

django/db/migrations/loader.py

@@ -133,7 +133,7 @@ class MigrationLoader:
             raise AmbiguityError(
                 "There is more than one migration for '%s' with the prefix '%s'" % (app_label, name_prefix)
             )
-        elif len(results) == 0:
+        elif not results:
             raise KeyError("There no migrations for '%s' with the prefix '%s'" % (app_label, name_prefix))
         else:
             return self.disk_migrations[results[0]]

django/db/migrations/questioner.py

@@ -85,7 +85,7 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
         result = input("%s " % question)
         if not result and default is not None:
             return default
-        while len(result) < 1 or result[0].lower() not in "yn":
+        while not result or result[0].lower() not in "yn":
             result = input("Please answer yes or no: ")
         return result[0].lower() == "y"
 

django/db/migrations/topological_sort.py

@@ -10,7 +10,7 @@ def topological_sort_as_sets(dependency_graph):
     """
     todo = dependency_graph.copy()
     while todo:
-        current = {node for node, deps in todo.items() if len(deps) == 0}
+        current = {node for node, deps in todo.items() if not deps}
 
         if not current:
             raise ValueError('Cyclic dependency in graph: {}'.format(

django/db/models/base.py

@@ -583,7 +583,7 @@ class Model(metaclass=ModelBase):
         of the field will call this method.
         """
         if fields is not None:
-            if len(fields) == 0:
+            if not fields:
                 return
             if any(LOOKUP_SEP in f for f in fields):
                 raise ValueError(
@@ -688,7 +688,7 @@ class Model(metaclass=ModelBase):
             # If update_fields is empty, skip the save. We do also check for
             # no-op saves later on for inheritance cases. This bailout is
             # still needed for skipping signal sending.
-            if len(update_fields) == 0:
+            if not update_fields:
                 return
 
             update_fields = frozenset(update_fields)
@@ -736,7 +736,7 @@ class Model(metaclass=ModelBase):
         """
         using = using or router.db_for_write(self.__class__, instance=self)
         assert not (force_insert and (force_update or update_fields))
-        assert update_fields is None or len(update_fields) > 0
+        assert update_fields is None or update_fields
         cls = origin = self.__class__
         # Skip proxies, but keep the origin as the proxy model.
         if cls._meta.proxy:

django/db/models/expressions.py

@@ -161,7 +161,7 @@ class BaseExpression:
         return []
 
     def set_source_expressions(self, exprs):
-        assert len(exprs) == 0
+        assert not exprs
 
     def _parse_expressions(self, *expressions):
         return [
@@ -780,7 +780,7 @@ class ExpressionList(Func):
     template = '%(expressions)s'
 
     def __init__(self, *expressions, **extra):
-        if len(expressions) == 0:
+        if not expressions:
             raise ValueError('%s requires at least one expression.' % self.__class__.__name__)
         super().__init__(*expressions, **extra)
 

django/db/models/fields/related.py

@@ -600,7 +600,7 @@ class ForeignObject(RelatedField):
         return name, path, args, kwargs
 
     def resolve_related_fields(self):
-        if len(self.from_fields) < 1 or len(self.from_fields) != len(self.to_fields):
+        if not self.from_fields or len(self.from_fields) != len(self.to_fields):
             raise ValueError('Foreign Object from and to fields must be the same non-zero length')
         if isinstance(self.remote_field.model, str):
             raise ValueError('Related model %r cannot be resolved' % self.remote_field.model)
@@ -1165,7 +1165,7 @@ class ManyToManyField(RelatedField):
                 )
             )
 
-        if len(self._validators) > 0:
+        if self._validators:
             warnings.append(
                 checks.Warning(
                     'ManyToManyField does not support validators.',

django/db/models/query.py

@@ -1433,7 +1433,7 @@ def prefetch_related_objects(model_instances, *related_lookups):
     Populate prefetched object caches for a list of model instances based on
     the lookups/Prefetch instances given.
     """
-    if len(model_instances) == 0:
+    if not model_instances:
         return  # nothing to do
 
     # We need to be able to dynamically add to the list of prefetch_related
@@ -1461,7 +1461,7 @@ def prefetch_related_objects(model_instances, *related_lookups):
         through_attrs = lookup.prefetch_through.split(LOOKUP_SEP)
         for level, through_attr in enumerate(through_attrs):
             # Prepare main instances
-            if len(obj_list) == 0:
+            if not obj_list:
                 break
 
             prefetch_to = lookup.get_current_prefetch_to(level)

django/db/models/sql/query.py

@@ -1061,7 +1061,7 @@ class Query:
         and get_transform().
         """
         # __exact is the default lookup if one isn't given.
-        if len(lookups) == 0:
+        if not lookups:
             lookups = ['exact']
 
         for name in lookups[:-1]:

django/forms/models.py

@@ -1006,7 +1006,7 @@ def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
                 raise ValueError(
                     "fk_name '%s' is not a ForeignKey to '%s'." % (fk_name, parent_model._meta.label)
                 )
-        elif len(fks_to_parent) == 0:
+        elif not fks_to_parent:
             raise ValueError(
                 "'%s' has no field named '%s'." % (model._meta.label, fk_name)
             )
@@ -1021,7 +1021,7 @@ def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
         ]
         if len(fks_to_parent) == 1:
             fk = fks_to_parent[0]
-        elif len(fks_to_parent) == 0:
+        elif not fks_to_parent:
             if can_fail:
                 return
             raise ValueError(

django/template/defaultfilters.py

@@ -568,7 +568,7 @@ def slice_filter(value, arg):
     try:
         bits = []
         for x in arg.split(':'):
-            if len(x) == 0:
+            if not x:
                 bits.append(None)
             else:
                 bits.append(int(x))

django/template/defaulttags.py

@@ -715,7 +715,7 @@ def firstof(parser, token):
     """
     bits = token.split_contents()[1:]
     asvar = None
-    if len(bits) < 1:
+    if not bits:
         raise TemplateSyntaxError("'firstof' statement requires at least one argument")
 
     if len(bits) >= 2 and bits[-2] == 'as':
@@ -1363,7 +1363,7 @@ def url(parser, token):
         asvar = bits[-1]
         bits = bits[:-2]
 
-    if len(bits):
+    if bits:
         for bit in bits:
             match = kwarg_re.match(bit)
             if not match:

django/test/testcases.py

@@ -114,11 +114,12 @@ class _AssertTemplateUsedContext:
 
         if not self.test():
             message = self.message()
-            if len(self.rendered_templates) == 0:
+            if self.rendered_templates:
-                message += ' No template was rendered.'
-            else:
                 message += ' Following templates were rendered: %s' % (
-                    ', '.join(self.rendered_template_names))
+                    ', '.join(self.rendered_template_names)
+                )
+            else:
+                message += ' No template was rendered.'
             self.test_case.fail(message)
 
 
@@ -255,7 +256,7 @@ class SimpleTestCase(unittest.TestCase):
         if hasattr(response, 'redirect_chain'):
             # The request was a followed redirect
             self.assertTrue(
-                len(response.redirect_chain) > 0,
+                response.redirect_chain,
                 msg_prefix + "Response didn't redirect as expected: Response code was %d (expected %d)"
                 % (response.status_code, status_code)
             )
@@ -488,7 +489,7 @@ class SimpleTestCase(unittest.TestCase):
                 elif form_index is not None:
                     non_field_errors = context[formset].forms[form_index].non_field_errors()
                     self.assertFalse(
-                        len(non_field_errors) == 0,
+                        not non_field_errors,
                         msg_prefix + "The formset '%s', form %d in context %d "
                         "does not contain any non-field errors." % (formset, form_index, i)
                     )
@@ -501,7 +502,7 @@ class SimpleTestCase(unittest.TestCase):
                 else:
                     non_form_errors = context[formset].non_form_errors()
                     self.assertFalse(
-                        len(non_form_errors) == 0,
+                        not non_form_errors,
                         msg_prefix + "The formset '%s' in context %d does not "
                         "contain any non-form errors." % (formset, i)
                     )
@@ -602,7 +603,7 @@ class SimpleTestCase(unittest.TestCase):
             kwargs: Extra kwargs.
         """
         callable_obj = None
-        if len(args):
+        if args:
             callable_obj = args[0]
             args = args[1:]
 

django/urls/resolvers.py

@@ -379,7 +379,7 @@ class URLResolver:
         self._local = threading.local()
 
     def __repr__(self):
-        if isinstance(self.urlconf_name, list) and len(self.urlconf_name):
+        if isinstance(self.urlconf_name, list) and self.urlconf_name:
             # Don't bother to output the whole list, it can be huge
             urlconf_repr = '<%s list>' % self.urlconf_name[0].__class__.__name__
         else:

django/utils/http.py

@@ -420,7 +420,7 @@ def limited_parse_qsl(qs, keep_blank_values=False, encoding='utf-8',
                 nv.append('')
             else:
                 continue
-        if len(nv[1]) or keep_blank_values:
+        if nv[1] or keep_blank_values:
             name = nv[0].replace('+', ' ')
             name = unquote(name, encoding=encoding, errors=errors)
             value = nv[1].replace('+', ' ')

django/utils/text.py

@@ -247,7 +247,7 @@ def get_text_list(list_, last_word=gettext_lazy('or')):
     >>> get_text_list([])
     ''
     """
-    if len(list_) == 0:
+    if not list_:
         return ''
     if len(list_) == 1:
         return str(list_[0])

django/utils/translation/trans_real.py

@@ -304,15 +304,15 @@ def gettext(message):
 
     eol_message = message.replace('\r\n', '\n').replace('\r', '\n')
 
-    if len(eol_message) == 0:
+    if eol_message:
-        # Return an empty value of the corresponding type if an empty message
-        # is given, instead of metadata, which is the default gettext behavior.
-        result = type(message)("")
-    else:
         _default = _default or translation(settings.LANGUAGE_CODE)
         translation_object = getattr(_active, "value", _default)
 
         result = translation_object.gettext(eol_message)
+    else:
+        # Return an empty value of the corresponding type if an empty message
+        # is given, instead of metadata, which is the default gettext behavior.
+        result = type(message)('')
 
     if isinstance(message, SafeData):
         return mark_safe(result)

django/views/generic/dates.py

@@ -333,7 +333,7 @@ class BaseDateListView(MultipleObjectMixin, DateMixin, View):
         if not allow_empty:
             # When pagination is enabled, it's better to do a cheap query
             # than to load the unpaginated queryset in memory.
-            is_empty = len(qs) == 0 if paginate_by is None else not qs.exists()
+            is_empty = not qs if paginate_by is None else not qs.exists()
             if is_empty:
                 raise Http404(_("No %(verbose_name_plural)s available") % {
                     'verbose_name_plural': qs.model._meta.verbose_name_plural,

django/views/generic/list.py

@@ -149,7 +149,7 @@ class BaseListView(MultipleObjectMixin, View):
             if self.get_paginate_by(self.object_list) is not None and hasattr(self.object_list, 'exists'):
                 is_empty = not self.object_list.exists()
             else:
-                is_empty = len(self.object_list) == 0
+                is_empty = not self.object_list
             if is_empty:
                 raise Http404(_("Empty list and '%(class_name)s.allow_empty' is False.") % {
                     'class_name': self.__class__.__name__,

docs/_ext/djangodocs.py

@@ -277,7 +277,7 @@ class DjangoHTMLTranslator(HTMLTranslator):
         if version_text:
             title = "%s%s" % (
                 version_text % node['version'],
-                ":" if len(node) else "."
+                ":" if node else "."
             )
             self.body.append('<span class="title">%s</span> ' % title)
 

tests/migrations/test_autodetector.py

@@ -1164,7 +1164,7 @@ class AutodetectorTests(TestCase):
 
         def test(from_state, to_state, msg):
             changes = self.get_changes([from_state], [to_state])
-            if len(changes) > 0:
+            if changes:
                 ops = ', '.join(o.__class__.__name__ for o in changes['a'][0].operations)
                 self.fail('Created operation(s) %s from %s' % (ops, msg))