Optimized Model instantiation a bit.

* Avoid some unnecessary attribute lookups, e.g. access signals directly rather than from module
* Alias some repeat accesses inside the method to use the slightly faster local lookups
* Use tuple to iterate remaining kwargs as it's faster to construct
* Cache Field.get_default() to avoid running through all the logic on every call
* Use a cached list of the properties on the model class to avoid repeat isinstance() calls

django/db/models/base.py

@@ -16,7 +16,6 @@ from django.db import (
     DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY, DatabaseError, connection,
     connections, router, transaction,
 )
-from django.db.models import signals
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.deletion import CASCADE, Collector
 from django.db.models.fields.related import (
@@ -25,6 +24,9 @@ from django.db.models.fields.related import (
 from django.db.models.manager import Manager
 from django.db.models.options import Options
 from django.db.models.query import Q
+from django.db.models.signals import (
+    class_prepared, post_init, post_save, pre_init, pre_save,
+)
 from django.db.models.utils import make_model_tuple
 from django.utils import six
 from django.utils.deprecation import RemovedInDjango20Warning
@@ -366,7 +368,7 @@ class ModelBase(type):
             manager.auto_created = True
             cls.add_to_class('objects', manager)
 
-        signals.class_prepared.send(sender=cls)
+        class_prepared.send(sender=cls)
 
     def _requires_legacy_default_manager(cls):  # RemovedInDjango20Warning
         opts = cls._meta
@@ -465,7 +467,13 @@ class ModelState(object):
 class Model(six.with_metaclass(ModelBase)):
 
     def __init__(self, *args, **kwargs):
-        signals.pre_init.send(sender=self.__class__, args=args, kwargs=kwargs)
+        # Alias some things as locals to avoid repeat global lookups
+        cls = self.__class__
+        opts = self._meta
+        _setattr = setattr
+        _DEFERRED = DEFERRED
+
+        pre_init.send(sender=cls, args=args, kwargs=kwargs)
 
         # Set up the storage for instance state
         self._state = ModelState()
@@ -474,27 +482,27 @@ class Model(six.with_metaclass(ModelBase)):
         # overrides it. It should be one or the other; don't duplicate the work
         # The reason for the kwargs check is that standard iterator passes in by
         # args, and instantiation for iteration is 33% faster.
-        if len(args) > len(self._meta.concrete_fields):
+        if len(args) > len(opts.concrete_fields):
             # Daft, but matches old exception sans the err msg.
             raise IndexError("Number of args exceeds number of fields")
 
         if not kwargs:
-            fields_iter = iter(self._meta.concrete_fields)
+            fields_iter = iter(opts.concrete_fields)
             # The ordering of the zip calls matter - zip throws StopIteration
             # when an iter throws it. So if the first iter throws it, the second
             # is *not* consumed. We rely on this, so don't change the order
             # without changing the logic.
             for val, field in zip(args, fields_iter):
-                if val is DEFERRED:
+                if val is _DEFERRED:
                     continue
-                setattr(self, field.attname, val)
+                _setattr(self, field.attname, val)
         else:
             # Slower, kwargs-ready version.
-            fields_iter = iter(self._meta.fields)
+            fields_iter = iter(opts.fields)
             for val, field in zip(args, fields_iter):
-                if val is DEFERRED:
+                if val is _DEFERRED:
                     continue
-                setattr(self, field.attname, val)
+                _setattr(self, field.attname, val)
                 kwargs.pop(field.name, None)
 
         # Now we're left with the unprocessed fields that *must* come from
@@ -539,28 +547,28 @@ class Model(six.with_metaclass(ModelBase)):
                 # field.name instead of field.attname (e.g. "user" instead of
                 # "user_id") so that the object gets properly cached (and type
                 # checked) by the RelatedObjectDescriptor.
-                if rel_obj is not DEFERRED:
-                    setattr(self, field.name, rel_obj)
+                if rel_obj is not _DEFERRED:
+                    _setattr(self, field.name, rel_obj)
             else:
-                if val is not DEFERRED:
-                    setattr(self, field.attname, val)
+                if val is not _DEFERRED:
+                    _setattr(self, field.attname, val)
 
         if kwargs:
-            for prop in list(kwargs):
+            property_names = opts._property_names
+            for prop in tuple(kwargs):
                 try:
                     # Any remaining kwargs must correspond to properties or
                     # virtual fields.
-                    if (isinstance(getattr(self.__class__, prop), property) or
-                            self._meta.get_field(prop)):
-                        if kwargs[prop] is not DEFERRED:
-                            setattr(self, prop, kwargs[prop])
+                    if prop in property_names or opts.get_field(prop):
+                        if kwargs[prop] is not _DEFERRED:
+                            _setattr(self, prop, kwargs[prop])
                         del kwargs[prop]
                 except (AttributeError, FieldDoesNotExist):
                     pass
             if kwargs:
                 raise TypeError("'%s' is an invalid keyword argument for this function" % list(kwargs)[0])
         super(Model, self).__init__()
-        signals.post_init.send(sender=self.__class__, instance=self)
+        post_init.send(sender=cls, instance=self)
 
     @classmethod
     def from_db(cls, db, field_names, values):
@@ -816,8 +824,10 @@ class Model(six.with_metaclass(ModelBase)):
             cls = cls._meta.concrete_model
         meta = cls._meta
         if not meta.auto_created:
-            signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using,
-                                  update_fields=update_fields)
+            pre_save.send(
+                sender=origin, instance=self, raw=raw, using=using,
+                update_fields=update_fields,
+            )
         with transaction.atomic(using=using, savepoint=False):
             if not raw:
                 self._save_parents(cls, using, update_fields)
@@ -829,8 +839,10 @@ class Model(six.with_metaclass(ModelBase)):
 
         # Signal that the save is complete
         if not meta.auto_created:
-            signals.post_save.send(sender=origin, instance=self, created=(not updated),
-                                   update_fields=update_fields, raw=raw, using=using)
+            post_save.send(
+                sender=origin, instance=self, created=(not updated),
+                update_fields=update_fields, raw=raw, using=using,
+            )
 
     save_base.alters_data = True
 

django/db/models/fields/__init__.py

@@ -92,6 +92,10 @@ def _empty(of_cls):
     return new
 
 
+def return_None():
+    return None
+
+
 @total_ordering
 @python_2_unicode_compatible
 class Field(RegisterLookupMixin):
@@ -771,13 +775,18 @@ class Field(RegisterLookupMixin):
         """
         Returns the default value for this field.
         """
+        return self._get_default()
+
+    @cached_property
+    def _get_default(self):
         if self.has_default():
             if callable(self.default):
-                return self.default()
                 return self.default
+            return lambda: self.default
+
         if not self.empty_strings_allowed or self.null and not connection.features.interprets_empty_strings_as_nulls:
-            return None
-        return ""
+            return return_None
+        return six.text_type  # returns empty string
 
     def get_choices(self, include_blank=True, blank_choice=BLANK_CHOICE_DASH, limit_choices_to=None):
         """Returns choices with a default blank choices included, for use

django/db/models/options.py

@@ -883,3 +883,14 @@ class Options(object):
     @has_auto_field.setter
     def has_auto_field(self, value):
         pass
+
+    @cached_property
+    def _property_names(self):
+        """
+        Return a set of the names of the properties defined on the model.
+        Internal helper for model initialization.
+        """
+        return frozenset({
+            attr for attr in
+            dir(self.model) if isinstance(getattr(self.model, attr), property)
+        })