标签：python flask 源码
我觉得我已经养成了一个坏习惯，在使用一个框架过程中对它的内部原理非常感兴趣，有时候需要花不少精力才
明白，这也导致了学习的缓慢，但换来的是对框架的内部机理的熟悉，正如侯捷所说，源码面前，了无秘密。这也是
本文产生的直接原因。
def setup():
from ..exthook import ExtensionImporter
importer = ExtensionImporter([‘flask_%s‘, ‘flaskext.%s‘], __name__)
importer.install()install将会向sys.meta_path添加模块装载类，当import时会调用其find_module，如果返回非None,会调用load_module加载 def install(self):
sys.meta_path[:] = [x for x in sys.meta_path if self != x] + [self]
def find_module(self, fullname, path=None):
if fullname.startswith(self.prefix):
return self
def load_module(self, fullname):
modname = fullname.split(‘.‘, self.prefix_cutoff)[self.prefix_cutoff]
for path in self.module_choices:
realname = path % modname
__import__(realname) @teardown
def shutdown_session(response_or_exc):
if app.config[‘SQLALCHEMY_COMMIT_ON_TEARDOWN‘]:
if response_or_exc is None:
self.session.commit()
self.session.remove()
return response_or_excresponse_or_exc为异常值，默认为sys.exc_info()[1]class scoped_session(object):
def __init__(self, session_factory, scopefunc=None):
self.session_factory = session_factory
if scopefunc:
self.registry = ScopedRegistry(session_factory, scopefunc)
else:
self.registry = ThreadLocalRegistry(session_factory)
__init__中，session_factory是创建session的工厂函数，而sessionmaker就是一工厂函数(其实是定义了__call__的class ThreadLocalRegistry(ScopedRegistry):
def __init__(self, createfunc):
self.createfunc = createfunc
self.registry = threading.local()
def __call__(self):
try:
return self.registry.value
except AttributeError:
val = self.registry.v从上面__call__可以看出，每次都会创建新的session，并发在线程本地变量中，你可能会好奇__call__是在哪里调用的？def instrument(name):
def do(self, *args, **kwargs):
return getattr(self.registry(), name)(*args, **kwargs)
return do
for meth in Session.public_methods:
setattr(scoped_session, meth, instrument(meth))正如我们所看到的，当我们调用session.query将会调用 getattr(self.registry(), ‘query‘)，self.registry()就是# Which stack should we use? _app_ctx_stack is new in 0.9
connection_stack = _app_ctx_stack or _request_ctx_stack
def __init__(self, app=None,
use_native_unicode=True,
session_options=None):
session_options.setdefault(
‘scopefunc‘, connection_stack.__ident_func__
)
self.session = self.create_scoped_session(session_options)
def create_scoped_session(self, options=None):
"""Helper factory method that creates a scoped session."""
if options is None:
options = {}
scopefunc=options.pop(‘scopefunc‘, None)
return orm.scoped_session(
partial(_SignallingSession, self, **options), scopefunc=scopefunc
)我们看到scopefunc被设置为connection_stack.__ident_func__，而connection_stack就是flask中app上下文，class ScopedRegistry(object):
def __init__(self, createfunc, scopefunc):
self.createfunc = createfunc
self.scopefunc = scopefunc
self.registry = {}
def __call__(self):
key = self.scopefunc()
try:
return self.registry[key]
except KeyError:
return self.registry.setdefault(key, self.createfunc())代码也很简单，其实也就是根据线程id创建对应的session对象，到这里我们基本已经了解了flask_sqlalchemy的class Role(db.Model):
__tablename__ = ‘roles‘
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
users = db.relationship(‘User‘, backref=‘role‘, lazy=‘dynamic‘)
class User(db.Model):
__tablename__ = ‘users‘
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(64), unique=True, index=True)
role_id = db.Column(db.Integer, db.ForeignKey(‘roles.id‘))假设role是已经获取的一个Role的实例{% block scripts %}
{{ super() }}
{{ moment.include_moment() }}
{{ moment.lang(‘zh-cn‘) }}
{% endblock %}flask moment还提供了过了多长时间统计，refresh为True时，每分钟刷新一次，refresh也可为具体的刷新时间， def init_app(self, app):
if not hasattr(app, ‘extensions‘):
app.extensions = {}
app.extensions[‘moment‘] = _moment
app.context_processor(self.context_processor)
@staticmethod
def context_processor():
return {
‘moment‘: current_app.extensions[‘moment‘]
}通过app.context_processor给模板上下文添加了额为属性rv.globals.update(
url_for=url_for,
get_flashed_messages=get_flashed_messages,
config=self.config,
# request, session and g are normally added with the
# context processor for efficiency reasons but for imported
# templates we also want the proxies in there.
request=request,
session=session,
g=g
)但我在看源码时发现_default_template_ctx_processor也会注入g，request，如下def _default_template_ctx_processor():
"""Default template context processor. Injects `request`,
`session` and `g`.
"""
reqctx = _request_ctx_stack.top
appctx = _app_ctx_stack.top
rv = {}
if appctx is not None:
rv[‘g‘] = appctx.g
if reqctx is not None:
rv[‘request‘] = reqctx.request
rv[‘session‘] = reqctx.session
return rv这不是重复嘛，有啥必要呢？标签：python flask 源码
原文地址：http://blog.csdn.net/yueguanghaidao/article/details/40016235
