django app注册过程
相关知识
sys.modules[__name__]获取本模块
collections是Python内建的一个集合模块，提供了许多有用的集合类。
namedtuple
namedtuple是一个函数，它用来创建一个自定义的tuple对象，并且规定了tuple元素的个数，并可以用属性而不是索引来引用tuple的某个元素。
这样一来，我们用namedtuple可以很方便地定义一种数据类型，它具备tuple的不变性，又可以根据属性来引用，使用十分方便。
deque
使用list存储数据时，按索引访问元素很快，但是插入和删除元素就很慢了，因为list是线性存储，数据量大的时候，插入和删除效率很低。
deque是为了高效实现插入和删除操作的双向列表，适合用于队列和栈
defaultdict
使用dict时，如果引用的Key不存在，就会抛出KeyError。如果希望key不存在时，返回一个默认值，就可以用defaultdict
OrderedDict
使用dict时，Key是无序的。在对dict做迭代时，我们无法确定Key的顺序。
Counter
Counter是一个简单的计数器，例如，统计字符出现的个数：
字符串函数rpartition与partition
这两个函数都接收一个分割字符串作为参数，将目标字符串分割为两个部分，返回一个三元元组（head,sep,tail），包含分割符。细微区别在于前者从目标字符串的末尾也就是右边开始搜索分割符。
def setup(set_prefix=True):
"""
Configure the settings (this happens as a side effect of accessing the
first setting), configure logging and populate the app registry.
Set the thread-local urlresolvers script prefix if `set_prefix` is True.
"""
from django.apps import apps
from django.conf import settings
from django.urls import set_script_prefix
from django.utils.encoding import force_text
from django.utils.log import configure_logging
configure_logging(settings.LOGGING_CONFIG, settings.LOGGING)
if set_prefix:
set_script_prefix(
'/' if settings.FORCE_SCRIPT_NAME is None else force_text(settings.FORCE_SCRIPT_NAME)
)
apps.populate(settings.INSTALLED_APPS)#注册app
class Apps(object):
"""
A registry that stores the configuration of installed applications.
It also keeps track of models eg. to provide reverse-relations.
"""
def __init__(self, installed_apps=()):
# installed_apps is set to None when creating the master registry
# because it cannot be populated at that point. Other registries must
# provide a list of installed apps and are populated immediately.
if installed_apps is None and hasattr(sys.modules[__name__], 'apps'):
raise RuntimeError("You must supply an installed_apps argument.")
# Mapping of app labels => model names => model classes. Every time a
# model is imported, ModelBase.__new__ calls apps.register_model which
# creates an entry in all_models. All imported models are registered,
# regardless of whether they're defined in an installed application
# and whether the registry has been populated. Since it isn't possible
# to reimport a module safely (it could reexecute initialization code)
# all_models is never overridden or reset.
self.all_models = defaultdict(OrderedDict)
# Mapping of labels to AppConfig instances for installed apps.
self.app_configs = OrderedDict()
# Stack of app_configs. Used to store the current state in
# set_available_apps and set_installed_apps.
self.stored_app_configs = []
# Whether the registry is populated.
self.apps_ready = self.models_ready = self.ready = False
# Lock for thread-safe population.
self._lock = threading.Lock()
# Maps ("app_label", "modelname") tuples to lists of functions to be
# called when the corresponding model is ready. Used by this class's
# `lazy_model_operation()` and `do_pending_operations()` methods.
self._pending_operations = defaultdict(list)
# Populate apps and models, unless it's the master registry.
if installed_apps is not None:
self.populate(installed_apps)
def populate(self, installed_apps=None):
"""
Loads application configurations and models.
This method imports each application module and then each model module.
It is thread safe and idempotent, but not reentrant.
"""
if self.ready:
return
# populate() might be called by two threads in parallel on servers
# that create threads before initializing the WSGI callable.
with self._lock:
if self.ready:
return
# app_config should be pristine, otherwise the code below won't
# guarantee that the order matches the order in INSTALLED_APPS.
if self.app_configs:
raise RuntimeError("populate() isn't reentrant")
# Phase 1: initialize app configs and import app modules.
for entry in installed_apps:
if isinstance(entry, AppConfig):
app_config = entry
else:
app_config = AppConfig.create(entry)
if app_config.label in self.app_configs:
raise ImproperlyConfigured(
"Application labels aren't unique, "
"duplicates: %s" % app_config.label)
self.app_configs[app_config.label] = app_config
app_config.apps = self#改变了自身，完成注册可以通过apps管理
# Check for duplicate app names.
counts = Counter(
app_config.name for app_config in self.app_configs.values())
duplicates = [
name for name, count in counts.most_common() if count > 1]
if duplicates:
raise ImproperlyConfigured(
"Application names aren't unique, "
"duplicates: %s" % ", ".join(duplicates))
self.apps_ready = True
# Phase 2: import models modules.
for app_config in self.app_configs.values():
app_config.import_models()
self.clear_cache()
self.models_ready = True
# Phase 3: run ready() methods of app configs.
for app_config in self.get_app_configs():
app_config.ready()
self.ready = True
@classmethod#工厂方法
def create(cls, entry):
"""
Factory that creates an app config from an entry in INSTALLED_APPS.
"""
try:
# If import_module succeeds, entry is a path to an app module,
# which may specify an app config class with default_app_config.
# Otherwise, entry is a path to an app config class or an error.
module = import_module(entry)
except ImportError:
# Track that importing as an app module failed. If importing as an
# app config class fails too, we'll trigger the ImportError again.
module = None
mod_path, _, cls_name = entry.rpartition('.')
# Raise the original exception when entry cannot be a path to an
# app config class.
if not mod_path:
raise
else:
try:
# If this works, the app module specifies an app config class.
entry = module.default_app_config
except AttributeError:
# Otherwise, it simply uses the default app config class.
return cls(entry, module)
else:
mod_path, _, cls_name = entry.rpartition('.')
# If we're reaching this point, we must attempt to load the app config
# class located at <mod_path>.<cls_name>
mod = import_module(mod_path)
try:
cls = getattr(mod, cls_name)
except AttributeError:
if module is None:
# If importing as an app module failed, that error probably
# contains the most informative traceback. Trigger it again.
import_module(entry)
else:
raise
# Check for obvious errors. (This check prevents duck typing, but
# it could be removed if it became a problem in practice.)
if not issubclass(cls, AppConfig):
raise ImproperlyConfigured(
"'%s' isn't a subclass of AppConfig." % entry)
# Obtain app name here rather than in AppClass.__init__ to keep
# all error checking for entries in INSTALLED_APPS in one place.
try:
app_name = cls.name
except AttributeError:
raise ImproperlyConfigured(
"'%s' must supply a name attribute." % entry)
# Ensure app_name points to a valid module.
try:
app_module = import_module(app_name)
except ImportError:
raise ImproperlyConfigured(
"Cannot import '%s'. Check that '%s.%s.name' is correct." % (
app_name, mod_path, cls_name,
)
)
# Entry is a path to an app config class.
return cls(app_name, app_module)通过模块名，类函数静态方法创建工程函数，