Avoided creating temporary lists for obtaining the first item.

django/db/migrations/loader.py

@@ -156,9 +156,9 @@ class MigrationLoader:
         if key[0] in self.migrated_apps:
             try:
                 if key[1] == "__first__":
-                    return list(self.graph.root_nodes(key[0]))[0]
+                    return self.graph.root_nodes(key[0])[0]
                 else:  # "__latest__"
-                    return list(self.graph.leaf_nodes(key[0]))[0]
+                    return self.graph.leaf_nodes(key[0])[0]
             except IndexError:
                 if self.ignore_no_migrations:
                     return None

django/db/migrations/questioner.py

@@ -48,7 +48,7 @@ class MigrationQuestioner:
             elif hasattr(migrations_module, "__path__"):
                 if len(migrations_module.__path__) > 1:
                     return False
-                filenames = os.listdir(list(migrations_module.__path__)[0])
+                filenames = os.listdir(migrations_module.__path__[0])
             return not any(x.endswith(".py") for x in filenames if x != "__init__.py")
 
     def ask_not_null_addition(self, field_name, model_name):

django/db/models/base.py

@@ -481,8 +481,8 @@ class Model(metaclass=ModelBase):
                         del kwargs[prop]
                 except (AttributeError, FieldDoesNotExist):
                     pass
-            if kwargs:
-                raise TypeError("'%s' is an invalid keyword argument for this function" % list(kwargs)[0])
+            for kwarg in kwargs:
+                raise TypeError("'%s' is an invalid keyword argument for this function" % kwarg)
         super().__init__()
         post_init.send(sender=cls, instance=self)
 

django/db/models/query.py

@@ -275,7 +275,8 @@ class QuerySet:
 
         qs = self._clone()
         qs.query.set_limits(k, k + 1)
-        return list(qs)[0]
+        qs._fetch_all()
+        return qs._result_cache[0]
 
     def __and__(self, other):
         self._merge_sanity_check(other)
@@ -548,17 +549,13 @@ class QuerySet:
 
     def first(self):
         """Return the first object of a query or None if no match is found."""
-        objects = list((self if self.ordered else self.order_by('pk'))[:1])
-        if objects:
-            return objects[0]
-        return None
+        for obj in (self if self.ordered else self.order_by('pk'))[:1]:
+            return obj
 
     def last(self):
         """Return the last object of a query or None if no match is found."""
-        objects = list((self.reverse() if self.ordered else self.order_by('-pk'))[:1])
-        if objects:
-            return objects[0]
-        return None
+        for obj in (self.reverse() if self.ordered else self.order_by('-pk'))[:1]:
+            return obj
 
     def in_bulk(self, id_list=None, *, field_name='pk'):
         """

django/db/models/sql/query.py

@@ -217,7 +217,8 @@ class Query:
 
     @cached_property
     def base_table(self):
-        return list(self.alias_map)[0] if self.alias_map else None
+        for alias in self.alias_map:
+            return alias
 
     def __str__(self):
         """

django/forms/utils.py

@@ -95,7 +95,7 @@ class ErrorList(UserList, list):
     def get_json_data(self, escape_html=False):
         errors = []
         for error in self.as_data():
-            message = list(error)[0]
+            message = next(iter(error))
             errors.append({
                 'message': escape(message) if escape_html else message,
                 'code': error.code or '',
@@ -133,7 +133,7 @@ class ErrorList(UserList, list):
     def __getitem__(self, i):
         error = self.data[i]
         if isinstance(error, ValidationError):
-            return list(error)[0]
+            return next(iter(error))
         return error
 
     def __reduce_ex__(self, *args, **kwargs):

django/templatetags/i18n.py

@@ -500,7 +500,7 @@ def do_block_translate(parser, token):
         options[option] = value
 
     if 'count' in options:
-        countervar, counter = list(options['count'].items())[0]
+        countervar, counter = next(iter(options['count'].items()))
     else:
         countervar, counter = None, None
     if 'context' in options:

tests/get_earliest_or_latest/tests.py

@@ -155,7 +155,7 @@ class TestFirstLast(TestCase):
             # We know that we've broken the __iter__ method, so the queryset
             # should always raise an exception.
             with self.assertRaises(IndexError):
-                IndexErrorArticle.objects.all()[0]
+                IndexErrorArticle.objects.all()[:10:2]
             with self.assertRaises(IndexError):
                 IndexErrorArticle.objects.all().first()
             with self.assertRaises(IndexError):