感悟： 对Django源码进行分析主要来自两个方面的原因：
1、想熟悉django整个启动流程包括request请求到最后response响应以及中间环节的整个流程；
2、源于对一款开源的项目管理工具taiga,该工具采用前后端分离的架构，前端采用Angular Js（版本1.x），后端采用django rest framework框架。在后端代码的理解中看到了对比之前创建MTV架构的django项目更加方便、高效、合理的理念。因此想基于此项目对django框架有个基本的认识。
简述：
Django源码分析系列文章将会对从runserver启动，到加载用户配置文件、wsgi协议、url、router、中间件以及符合django rest framework框架的用户认证、权限管理、序列化、节流等众多功能模块进行详细的分析。本篇文章会暂对启动流程中加载用户配置文件以及安装app进行分析。
一、 manager.py main函数
django项目是从python manager.py runserver ip+port启动的，那么我们就深入源码理解启动逻辑。
#!/usr/bin/env python
"""Django's command-line utility for administrative tasks."""
import os
import sys
def main():
"""
django服务入口函数：
1、设置项目配置文件
2、执行runserver命令
"""
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'taiga_master.settings')
try:
from django.core.management import execute_from_command_line
except ImportError as exc:
raise ImportError(
"Couldn't import Django. Are you sure it's installed and "
"available on your PYTHONPATH environment variable? Did you "
"forget to activate a virtual environment?"
) from exc
"""
1、sys.argv：获取当前文件外部执行传递的参数列表
argv = ["...manager.py","runserver","ip:port"]
2、执行命令行参数
"""
execute_from_command_line(sys.argv)
if __name__ == '__main__':
main()
在manage.py的main函数主要进行两个操作：
1、第一个是将用户的项目设置路径，放入项目环境变量；
2、执行命令行参数(runserver ip+port)
二、execute_from_command_line(sys.argv) 执行命令行
def execute_from_command_line(argv=None):
"""Run a ManagementUtility."""
"管理模块参数赋值"
utility = ManagementUtility(argv)
"管理模块执行"
utility.execute()
三、** utility.execute()** 函数
def execute(self):
"""
Given the command-line arguments, figure out which subcommand is being
run, create a parser appropriate to that command, and run it.
"""
try:
subcommand = self.argv[1]
except IndexError:
subcommand = 'help' # Display help if no arguments were given.
# Preprocess options to extract --settings and --pythonpath.
# These options could affect the commands that are available, so they
# must be processed early.
parser = CommandParser(usage='%(prog)s subcommand [options] [args]', add_help=False, allow_abbrev=False)
parser.add_argument('--settings')
parser.add_argument('--pythonpath')
parser.add_argument('args', nargs='*') # catch-all
try:
options, args = parser.parse_known_args(self.argv[2:])
handle_default_options(options)
except CommandError:
pass # Ignore any option errors at this point.
try:
"获取settings里面的app列表，但是还未加载app"
settings.INSTALLED_APPS
except ImproperlyConfigured as exc:
self.settings_exception = exc
except ImportError as exc:
self.settings_exception = exc
if settings.configured:
# Start the auto-reloading dev server even if the code is broken.
# The hardcoded condition is a code smell but we can't rely on a
# flag on the command class because we haven't located it yet.
if subcommand == 'runserver' and '--noreload' not in self.argv:
try:
"在django.setup里面真正加载并检测app格式"
autoreload.check_errors(django.setup)()
except Exception:
# The exception will be raised later in the child process
# started by the autoreloader. Pretend it didn't happen by
# loading an empty list of applications.
apps.all_models = defaultdict(OrderedDict)
apps.app_configs = OrderedDict()
apps.apps_ready = apps.models_ready = apps.ready = True
# Remove options not compatible with the built-in runserver
# (e.g. options for the contrib.staticfiles' runserver).
# Changes here require manually testing as described in
# #27522.
_parser = self.fetch_command('runserver').create_parser('django', 'runserver')
_options, _args = _parser.parse_known_args(self.argv[2:])
for _arg in _args:
self.argv.remove(_arg)
# In all other cases, django.setup() is required to succeed.
else:
django.setup()
self.autocomplete()
if subcommand == 'help':
if '--commands' in args:
sys.stdout.write(self.main_help_text(commands_only=True) + '\n')
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])
# Special-cases: We want 'django-admin --version' and
# 'django-admin --help' to work, for backwards compatibility.
elif subcommand == 'version' or self.argv[1:] == ['--version']:
sys.stdout.write(django.get_version() + '\n')
elif self.argv[1:] in (['--help'], ['-h']):
sys.stdout.write(self.main_help_text() + '\n')
else:
self.fetch_command(subcommand).run_from_argv(self.argv)
该函数代码非常重要，主要完成配置文件加载以及app加载等功能。
1、settings.INSTALLED_APPS 这里涉及的知识点比较多，类似懒加载等
2、autoreload.check_errors(django.setup)()里面的django.setup
三、settings.INSTALLED_APPS 导入用户配置
# 懒加载
settings = LazySettings()
class LazySettings(LazyObject):
"""
A lazy proxy for either global Django settings or a custom settings object.
The user can manually configure settings prior to using them. Otherwise,
Django uses the settings module pointed to by DJANGO_SETTINGS_MODULE.
"""
def _setup(self, name=None):
"""
Load the settings module pointed to by the environment variable. This
is used the first time settings are needed, if the user hasn't
configured settings manually.
"""
settings_module = os.environ.get(ENVIRONMENT_VARIABLE)
if not settings_module:
desc = ("setting %s" % name) if name else "settings"
raise ImproperlyConfigured(
"Requested %s, but settings are not configured. "
"You must either define the environment variable %s "
"or call settings.configure() before accessing settings."
% (desc, ENVIRONMENT_VARIABLE))
self._wrapped = Settings(settings_module)
def __repr__(self):
# Hardcode the class name as otherwise it yields 'Settings'.
if self._wrapped is empty:
return '<LazySettings [Unevaluated]>'
return '<LazySettings "%(settings_module)s">' % {
'settings_module': self._wrapped.SETTINGS_MODULE,
}
def __getattr__(self, name):
"""Return the value of a setting and cache it in self.__dict__."""
if self._wrapped is empty:
self._setup(name)
val = getattr(self._wrapped, name)
self.__dict__[name] = val
return val
def __setattr__(self, name, value):
"""
Set the value of setting. Clear all cached values if _wrapped changes
(@override_settings does this) or clear single values when set.
"""
if name == '_wrapped':
self.__dict__.clear()
else:
self.__dict__.pop(name, None)
super().__setattr__(name, value)
def __delattr__(self, name):
"""Delete a setting and clear it from cache if needed."""
super().__delattr__(name)
self.__dict__.pop(name, None)
def configure(self, default_settings=global_settings, **options):
"""
Called to manually configure the settings. The 'default_settings'
parameter sets where to retrieve any unspecified values from (its
argument must support attribute access (__getattr__)).
"""
if self._wrapped is not empty:
raise RuntimeError('Settings already configured.')
holder = UserSettingsHolder(default_settings)
for name, value in options.items():
setattr(holder, name, value)
self._wrapped = holder
@property
def configured(self):
"""Return True if the settings have already been configured."""
return self._wrapped is not empty
@property
def DEFAULT_CONTENT_TYPE(self):
stack = traceback.extract_stack()
# Show a warning if the setting is used outside of Django.
# Stack index: -1 this line, -2 the caller.
filename, _line_number, _function_name, _text = stack[-2]
if not filename.startswith(os.path.dirname(django.__file__)):
warnings.warn(
DEFAULT_CONTENT_TYPE_DEPRECATED_MSG,
RemovedInDjango30Warning,
stacklevel=2,
)
return self.__getattr__('DEFAULT_CONTENT_TYPE')
@property
def FILE_CHARSET(self):
stack = traceback.extract_stack()
# Show a warning if the setting is used outside of Django.
# Stack index: -1 this line, -2 the caller.
filename, _line_number, _function_name, _text = stack[-2]
if not filename.startswith(os.path.dirname(django.__file__)):
warnings.warn(
FILE_CHARSET_DEPRECATED_MSG,
RemovedInDjango31Warning,
stacklevel=2,
)
return self.__getattr__('FILE_CHARSET')
class LazyObject:
"""
A wrapper for another class that can be used to delay instantiation of the
wrapped class.
By subclassing, you have the opportunity to intercept and alter the
instantiation. If you don't need to do that, use SimpleLazyObject.
"""
# Avoid infinite recursion when tracing __init__ (#19456).
_wrapped = None
def __init__(self):
# Note: if a subclass overrides __init__(), it will likely need to
# override __copy__() and __deepcopy__() as well.
self._wrapped = empty
__getattr__ = new_method_proxy(getattr)
def __setattr__(self, name, value):
if name == "_wrapped":
# Assign to __dict__ to avoid infinite __setattr__ loops.
self.__dict__["_wrapped"] = value
else:
if self._wrapped is empty:
self._setup()
setattr(self._wrapped, name, value)
def __delattr__(self, name):
if name == "_wrapped":
raise TypeError("can't delete _wrapped.")
if self._wrapped is empty:
self._setup()
delattr(self._wrapped, name)
def _setup(self):
"""
Must be implemented by subclasses to initialize the wrapped object.
"""
raise NotImplementedError('subclasses of LazyObject must provide a _setup() method')
# Because we have messed with __class__ below, we confuse pickle as to what
# class we are pickling. We're going to have to initialize the wrapped
# object to successfully pickle it, so we might as well just pickle the
# wrapped object since they're supposed to act the same way.
#
# Unfortunately, if we try to simply act like the wrapped object, the ruse
# will break down when pickle gets our id(). Thus we end up with pickle
# thinking, in effect, that we are a distinct object from the wrapped
# object, but with the same __dict__. This can cause problems (see #25389).
#
# So instead, we define our own __reduce__ method and custom unpickler. We
# pickle the wrapped object as the unpickler's argument, so that pickle
# will pickle it normally, and then the unpickler simply returns its
# argument.
def __reduce__(self):
if self._wrapped is empty:
self._setup()
return (unpickle_lazyobject, (self._wrapped,))
def __copy__(self):
if self._wrapped is empty:
# If uninitialized, copy the wrapper. Use type(self), not
# self.__class__, because the latter is proxied.
return type(self)()
else:
# If initialized, return a copy of the wrapped object.
return copy.copy(self._wrapped)
def __deepcopy__(self, memo):
if self._wrapped is empty:
# We have to use type(self), not self.__class__, because the
# latter is proxied.
result = type(self)()
memo[id(self)] = result
return result
return copy.deepcopy(self._wrapped, memo)
__bytes__ = new_method_proxy(bytes)
__str__ = new_method_proxy(str)
__bool__ = new_method_proxy(bool)
# Introspection support
__dir__ = new_method_proxy(dir)
# Need to pretend to be the wrapped class, for the sake of objects that
# care about this (especially in equality tests)
__class__ = property(new_method_proxy(operator.attrgetter("__class__")))
__eq__ = new_method_proxy(operator.eq)
__lt__ = new_method_proxy(operator.lt)
__gt__ = new_method_proxy(operator.gt)
__ne__ = new_method_proxy(operator.ne)
__hash__ = new_method_proxy(hash)
# List/Tuple/Dictionary methods support
__getitem__ = new_method_proxy(operator.getitem)
__setitem__ = new_method_proxy(operator.setitem)
__delitem__ = new_method_proxy(operator.delitem)
__iter__ = new_method_proxy(iter)
__len__ = new_method_proxy(len)
__contains__ = new_method_proxy(operator.contains)
class Settings:
def __init__(self, settings_module):
# update this dict from global settings (but only for ALL_CAPS settings)
"加载系统的setting配置文件"
for setting in dir(global_settings):
if setting.isupper():
setattr(self, setting, getattr(global_settings, setting))
# store the settings module in case someone later cares
self.SETTINGS_MODULE = settings_module
mod = importlib.import_module(self.SETTINGS_MODULE)
tuple_settings = (
"INSTALLED_APPS",
"TEMPLATE_DIRS",
"LOCALE_PATHS",
)
self._explicit_settings = set()
"加载用户setting配置文件"
for setting in dir(mod):
if setting.isupper():
setting_value = getattr(mod, setting)
if (setting in tuple_settings and
not isinstance(setting_value, (list, tuple))):
raise ImproperlyConfigured("The %s setting must be a list or a tuple. " % setting)
setattr(self, setting, setting_value)
self._explicit_settings.add(setting)
if not self.SECRET_KEY:
raise ImproperlyConfigured("The SECRET_KEY setting must not be empty.")
if self.is_overridden('DEFAULT_CONTENT_TYPE'):
warnings.warn(DEFAULT_CONTENT_TYPE_DEPRECATED_MSG, RemovedInDjango30Warning)
if self.is_overridden('FILE_CHARSET'):
warnings.warn(FILE_CHARSET_DEPRECATED_MSG, RemovedInDjango31Warning)
if hasattr(time, 'tzset') and self.TIME_ZONE:
# When we can, attempt to validate the timezone. If we can't find
# this file, no check happens and it's harmless.
zoneinfo_root = Path('/usr/share/zoneinfo')
zone_info_file = zoneinfo_root.joinpath(*self.TIME_ZONE.split('/'))
if zoneinfo_root.exists() and not zone_info_file.exists():
raise ValueError("Incorrect timezone setting: %s" % self.TIME_ZONE)
# Move the time zone info into os.environ. See ticket #2315 for why
# we don't do this unconditionally (breaks Windows).
os.environ['TZ'] = self.TIME_ZONE
time.tzset()
def is_overridden(self, setting):
return setting in self._explicit_settings
def __repr__(self):
return '<%(cls)s "%(settings_module)s">' % {
'cls': self.__class__.__name__,
'settings_module': self.SETTINGS_MODULE,
}
代码解读：settings.INSTALLED_APPS
1、settings是实例化的一个对象，然后进入LazySettings类的__init__函数，发现该类没有__init__函数，则找其父类LazyObject，执行其里面的__init__函数，该函数内部发现self.wrapped = empty为空。到此完成实例化操作；
2、那么settings实例化操作后.INSTALLED_APPS，查找该类的INSTALLED_APPS的属性。到这里我们阐述一下python class里面的魔法方法。python类的魔法方法包含几个类别：比如构造初始化(init, new),属性访问控制（getattr, setattr,deleteattr,getattribute,）,描述器对象(get, set,delete)以及构造自定义的容器，在这里我们仅仅阐述我们用到的属性访问控制里面的__getattr_, setattr；
3、因为该类没有INSTALLED_APPS属性因此会进入__getattr__方法，在里面判断self._wrapped为空，进入self._setup(name)进行设置；
4、setup函数里面获取用户setting路径，然后执行self._wrapped = Settings(settings_module)
5、在Settings里面首先导入系统内部的配置，然后导入用户配置，重复的配置覆盖。到此用户的配置导入完毕，但是还未加载app以及对app进行检测。getattr 该方法定义了你试图访问一个不存在的属性时的行为。因此，重载该方法可以实现捕获错误拼写然后进行重定向, 或者对一些废弃的属性进行警告。
setattr 是实现封装的解决方案，它定义了你对属性进行赋值和修改操作时的行为。
不管对象的某个属性是否存在,它都允许你为该属性进行赋值,因此你可以为属性的值进行自定义操作。
四、 autoreload.check_errors(django.setup)() django初始化
from django.utils.version import get_version
VERSION = (2, 2, 11, 'final', 0)
__version__ = get_version(VERSION)
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.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 settings.FORCE_SCRIPT_NAME
)
"加载INSTALLED_APPS内app"
apps.populate(settings.INSTALLED_APPS)
def populate(self, installed_apps=None):
"""
Load application configurations and models.
Import 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
# An RLock prevents other threads from entering this section. The
# compare and set operation below is atomic.
if self.loading:
# Prevent reentrant calls to avoid running AppConfig.ready()
# methods twice.
raise RuntimeError("populate() isn't reentrant")
self.loading = True
# 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
# 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
self.ready_event.set()
该函数在for循环中AppConfig.create(entry)加载app，并更改加载状态。
到此完成用户配置文件setting的导入以及系统app和用户app的加载。