本人对flask源码整体分析（下）

Posted 2020-10-06 fuzzier

4 请求（request）

from flask import request

request接收了WSGI server 传递过来的 environ 字典变量，并提供了很多常用的属性和方法可以使用，比如请求的 method、path、args 等。

同时request还有一个特性——它不能被应用修改，应用只能读取请求的数据。

---> 4.1 Request(RequestBase)

其中 from werkzeug.wrappers import Request as RequestBase

该类继承 werkzeug的 request后，定义了一些 @property属性

　　---> werkzeug.wrappers:Request

class Request(BaseRequest, AcceptMixin, ETagRequestMixin,
              UserAgentMixin, AuthorizationMixin,
              CommonRequestDescriptorsMixin):

    """Full featured request object implementing the following mixins:

    - :class:`AcceptMixin` for accept header parsing
    - :class:`ETagRequestMixin` for etag and cache control handling
    - :class:`UserAgentMixin` for user agent introspection
    - :class:`AuthorizationMixin` for http auth handling
    - :class:`CommonRequestDescriptorsMixin` for common headers
    """

View Code

　　　　---> BaseRequest

class BaseRequest(object):
    def __init__(self, environ, populate_request=True, shallow=False):
        self.environ = environ
        if populate_request and not shallow:
            self.environ[‘werkzeug.request‘] = self
        self.shallow = shallow

　　　　主要就是传入了 self.environ 作为字段。
　　　　然后用 @cached_property 定义了一些属性， 像 args， form，  cookies等等
---> cached_property
接下来我们看看 增强版的 property

class cached_property(property):

    """A decorator that converts a function into a lazy property.  The
    function wrapped is called the first time to retrieve the result
    and then that calculated result is used the next time you access
    the value.

    The class has to have a `__dict__` in order for this property to
    work.
    """

    # implementation detail: A subclass of python‘s builtin property
    # decorator, we override __get__ to check for a cached value. If one
    # choses to invoke __get__ by hand the property will still work as
    # expected because the lookup logic is replicated in __get__ for
    # manual invocation.

    def __init__(self, func, name=None, doc=None):
        self.__name__ = name or func.__name__
        self.__module__ = func.__module__
        self.__doc__ = doc or func.__doc__
        self.func = func

    def __set__(self, obj, value):
        obj.__dict__[self.__name__] = value

    def __get__(self, obj, type=None):
        if obj is None:
            return self
        value = obj.__dict__.get(self.__name__, _missing)
        if value is _missing:
            value = self.func(obj)
            obj.__dict__[self.__name__] = value
        return value

View Code

这个装饰器同时也是实现了 __set__ 和 __get__ 方法的描述器。 访问它装饰的属性，就会调用 __get__ 方法，这个方法先在 obj.__dict__ 中寻找是否已经存在对应的值。如果存在，就直接返回；如果不存在，调用底层的函数 self.func，并把得到的值保存起来，再返回。这也是它能实现缓存的原因：因为它会把函数的值作为属性保存到对象中。 ---cizixs