from flask import get_request

# 獲取當(dāng)前request
request = get_request()
get_request().args

# File: flask/__init__.py
from .globals import current_app, g, request, session, _request_ctx_stack


# File: flask/globals.py
from functools import partial
from werkzeug.local import LocalStack, LocalProxy


def _lookup_req_object(name):
  top = _request_ctx_stack.top
  if top is None:
    raise RuntimeError('working outside of request context')
  return getattr(top, name)

# context locals
_request_ctx_stack = LocalStack()
request = LocalProxy(partial(_lookup_req_object, 'request'))

@implements_bool
class LocalProxy(object):
  """Acts as a proxy for a werkzeug local. Forwards all operations to
  a proxied object. The only operations not supported for forwarding
  are right handed operands and any kind of assignment.
  ... ...

# 為了方便說明，我對(duì)代碼進(jìn)行了一些刪減和改動(dòng)

@implements_bool
class LocalProxy(object):
  __slots__ = ('__local', '__dict__', '__name__')

  def __init__(self, local, name=None):
    # 這里有一個(gè)點(diǎn)需要注意一下，通過了__setattr__方法，self的
    # "_LocalProxy__local" 屬性被設(shè)置成了local，你可能會(huì)好奇
    # 這個(gè)屬性名稱為什么這么奇怪，其實(shí)這是因?yàn)镻ython不支持真正的
    # Private member，具體可以參見官方文檔：
    # http://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references
    # 在這里你只要把它當(dāng)做 self.__local = local 就可以了 :)
    object.__setattr__(self, '_LocalProxy__local', local)
    object.__setattr__(self, '__name__', name)

  def _get_current_object(self):
    """
    獲取當(dāng)前被代理的真正對(duì)象，一般情況下不會(huì)主動(dòng)調(diào)用這個(gè)方法，除非你因?yàn)?
    某些性能原因需要獲取做這個(gè)被代理的真正對(duì)象，或者你需要把它用來另外的
    地方。
    """
    # 這里主要是判斷代理的對(duì)象是不是一個(gè)werkzeug的Local對(duì)象，在我們分析request
    # 的過程中，不會(huì)用到這塊邏輯。
    if not hasattr(self.__local, '__release_local__'):
      # 從LocalProxy(partial(_lookup_req_object, 'request'))看來
      # 通過調(diào)用self.__local()方法，我們得到了 partial(_lookup_req_object, 'request')()
      # 也就是 ``_request_ctx_stack.top.request``
      return self.__local()
    try:
      return getattr(self.__local, self.__name__)
    except AttributeError:
      raise RuntimeError('no object bound to %s' % self.__name__)

  # 接下來就是一大段一段的Python的魔法方法了，Local Proxy重載了(幾乎)?所有Python
  # 內(nèi)建魔法方法，讓所有的關(guān)于他自己的operations都指向到了_get_current_object()
  # 所返回的對(duì)象，也就是真正的被代理對(duì)象。

  ... ...
  __setattr__ = lambda x, n, v: setattr(x._get_current_object(), n, v)
  __delattr__ = lambda x, n: delattr(x._get_current_object(), n)
  __str__ = lambda x: str(x._get_current_object())
  __lt__ = lambda x, o: x._get_current_object() < o
  __le__ = lambda x, o: x._get_current_object() <= o
  __eq__ = lambda x, o: x._get_current_object() == o
  __ne__ = lambda x, o: x._get_current_object() != o
  __gt__ = lambda x, o: x._get_current_object() > o
  __ge__ = lambda x, o: x._get_current_object() >= o
  ... ...

from functools import partial
from werkzeug.local import LocalStack, LocalProxy


def _lookup_req_object(name):
  top = _request_ctx_stack.top
  if top is None:
    raise RuntimeError('working outside of request context')
  return getattr(top, name)

# context locals
_request_ctx_stack = LocalStack()
request = LocalProxy(partial(_lookup_req_object, 'request'))

class LocalStack(object):

  def __init__(self):
    # 其實(shí)LocalStack主要還是用到了另外一個(gè)Local類
    # 它的一些關(guān)鍵的方法也被代理到了這個(gè)Local類上
    # 相對(duì)于Local類來說，它多實(shí)現(xiàn)了一些和堆棧“Stack”相關(guān)方法，比如push、pop之類
    # 所以，我們只要直接看Local代碼就可以
    self._local = Local()

  ... ...

  @property
  def top(self):
    """
    返回堆棧頂部的對(duì)象
    """
    try:
      return self._local.stack[-1]
    except (AttributeError, IndexError):
      return None


# 所以，當(dāng)我們調(diào)用_request_ctx_stack.top時(shí)，其實(shí)是調(diào)用了 _request_ctx_stack._local.stack[-1]
# 讓我們來看看Local類是怎么實(shí)現(xiàn)的吧，不過在這之前我們得先看一下下面出現(xiàn)的get_ident方法

# 首先嘗試著從greenlet導(dǎo)入getcurrent方法，這是因?yàn)槿绻鹒lask跑在了像gevent這種容器下的時(shí)候
# 所以的請(qǐng)求都是以greenlet作為最小單位，而不是thread線程。
try:
  from greenlet import getcurrent as get_ident
except ImportError:
  try:
    from thread import get_ident
  except ImportError:
    from _thread import get_ident

# 總之，這個(gè)get_ident方法將會(huì)返回當(dāng)前的協(xié)程/線程ID，這對(duì)于每一個(gè)請(qǐng)求都是唯一的


class Local(object):
  __slots__ = ('__storage__', '__ident_func__')

  def __init__(self):
    object.__setattr__(self, '__storage__', {})
    object.__setattr__(self, '__ident_func__', get_ident)

  ... ...

  # 問題的關(guān)鍵就在于Local類重載了__getattr__和__setattr__這兩個(gè)魔法方法

  def __getattr__(self, name):
    try:
      # 在這里我們返回調(diào)用了self.__ident_func__()，也就是當(dāng)前的唯一ID
      # 來作為__storage__的key
      return self.__storage__[self.__ident_func__()][name]
    except KeyError:
      raise AttributeError(name)

  def __setattr__(self, name, value):
    ident = self.__ident_func__()
    storage = self.__storage__
    try:
      storage[ident][name] = value
    except KeyError:
      storage[ident] = {name: value}

  ... ...

  # 重載了這兩個(gè)魔法方法之后

  # Local().some_value 不再是它看上去那么簡單了:
  # 首先我們先調(diào)用get_ident方法來獲取當(dāng)前運(yùn)行的線程/協(xié)程ID
  # 然后獲取這個(gè)ID空間下的some_value屬性，就像這樣：
  #
  #  Local().some_value -> Local()[current_thread_id()].some_value
  #
  # 設(shè)置屬性的時(shí)候也是這個(gè)道理