python with提前退出遇到的坑与解决方案

with CacheLock("test_lock", 10):
  #如果抢占到锁，那么就执行这段代码
  # 否则，让with提前退出

with CacheLock("test_lock", 10):
  value = cache.get("test_lock")
  self.assertEqual(value, 1)
  with CacheLock("test_lock", 10):
    # 不会进到这里
    self.assertFalse(True)
value = cache.get("test_lock")
self.assertEqual(value, None)

class CacheLock(object):
  def __init__(self, lock_key, lock_timeout):
    self.lock_key = lock_key
    self.lock_timeout = lock_timeout
    self.success = False
  def __enter__(self):
    self.success = cache.lock(self.lock_key, self.lock_timeout)
    if self.success:
      return self
    else:
      raise LockException("not have lock")
  def __exit__(self, exc_type, exc_value, traceback):
    #没有抢到锁的时候，啥都不做？
    if self.success:
      await cache.delete(self.lock_key)
    if isinstance(exc_value, LockException):
      return True
    if exc_type:
      raise exc_value

cache.set("test_lock",1)
with CacheLock("test_lock", 10):
  self.assertFalse(True)
value = cache.get("test_lock")
self.assertEqual(value, None)

import operator
class EarlyExit(Exception):
  pass
class ABContext(object):
  """AB测试上下文
  > with ABContext(newVersion, consts.ABEnum.layer2):
  >   # dosomething
  """
  def __init__(self, version, ab_layer, relationship="eq"):
    self.version = version
    self.ab_layer = ab_layer
    # 如果不存在这种操作符，那就提前报错
    self.relationship = getattr(operator, relationship)
  def __enter__(self):
    # 如果不满足条件，等于不执行上下文中的内容
    if not self.relationship(self.version, self.ab_layer.value):
      raise EarlyExit("not match")
    return self
  def __exit__(self, exc_type, exc_value, traceback):
    if exc_value is None:
      return True
    if isinstance(exc_value, EarlyExit):
      return True
    if exc_type:
      raise exc_value
    return True

def ensure(self):
    if not self.relationship(self.version, self.ab_layer.value):
      raise EarlyExit("not match")
  def __enter__(self):
    # 如果不满足条件，等于不执行上下文中的内容
    return self

with ABContext(newVersion, consts.ABEnum.layer2) as c:
  c.ensure()
  # 执行其他的想要执行的代码

from contextlib import nested
with nested(*managers):
  do_something()

from contextlib import nested
with nested(A(), B(), C()) as (X, Y, Z):
  do_something()
# is equivalent to this:
m1, m2, m3 = A(), B(), C()
with m1 as X:
  with m2 as Y:
    with m3 as Z:
      do_something()

with context1,context2:
  #do something

class AlwaySuccessContext(object):
  def __enter__(self):
    return self
  def __exit__(self, exc_type, exc_value, traceback):
    if isinstance(exc_value, EarlyExit):
      return True
    if exc_type:
      raise exc_value
    return True

def test_context_noteq(self):
    obj = MagicMock(return_value=True)
    with AlwaySuccessContext(), ABContext(2, const.ABTestEnum.control):
      self.assertFalse(obj())
    obj.assert_not_called()

def test_context_noteq(self):
    # 不等的时候，不会执行with里的内容
    obj = MagicMock(return_value=True)
    context = ABContext(2, const.ABTestEnum.control)
    # print(type(context))
    if ABContext(2, const.ABTestEnum.control):
      self.assertFalse(obj())
    obj.assert_not_called()