python 备忘（内置装饰器）

1. @classmethod ，加入这个装饰器表示第一个参数永远就是self

在stackoverflow看到的直接贴过来，有时候出现类似：required argument **cls** 可能是这个原因

2. @property ，加入这个装饰器表示把一个方法变成属性

1 class Foo:
 2     @property
 3     def AAA(self):
 4         print('get的时候运行我啊')
 5 
 6     @AAA.setter
 7     def AAA(self,value):
 8         print('set的时候运行我啊')
 9 
10     @AAA.deleter
11     def AAA(self):
12         print('delete的时候运行我啊')
13 
14 #只有在属性AAA定义property后才能定义AAA.setter,AAA.deleter
15 f1=Foo()
16 f1.AAA
17 f1.AAA='aaa'
18 del f1.AAA

3. @contextlib.contextmanager 装饰器，由它修饰的方法会有两部分构成，中间由yield关键字分开。在代码块执行前会先执行yield上面的语句；在代码块执行后会再执行yield下面的语句。

import contextlib
import time

@contextlib.contextmanager
def timeit():
    start = time.time()
    print('before yield ')
    yield start
    print('after yield stating')
    end = time.time()
    usedTime = (end - start) * 1000
    print ('Use time %d ms' % usedTime)
    print('after yield ending')

with timeit() as stattime:
    print('in with staring')
    time.sleep(1)
    print('in with doing something')
    print('in with ending')

'''
结果：
before yield 
in with staring
in with doing something
in with ending
after yield stating
Use time 1000 ms
after yield ending
'''

unittest 中的源码应用：
case.py中的with outcome.testPartExecutor(self) 会触发调用

'''
case.py
'''
with outcome.testPartExecutor(self):
      self._callSetUp()


'''
@contextlib.contextmanager的代码
'''
class _Outcome(object):
    def __init__(self, result=None):
        self.expecting_failure = False
        self.result = result
        self.result_supports_subtests = hasattr(result, "addSubTest")
        self.success = True
        self.skipped = []
        self.expectedFailure = None
        self.errors = []

    @contextlib.contextmanager
    def testPartExecutor(self, test_case, isTest=False):
        old_success = self.success
        self.success = True
        try:
            yield
        except KeyboardInterrupt:
            raise
        except SkipTest as e:
            self.success = False
            self.skipped.append((test_case, str(e)))
        except _ShouldStop:
            pass
        except:
            exc_info = sys.exc_info()
            if self.expecting_failure:
                self.expectedFailure = exc_info
            else:
                self.success = False
                self.errors.append((test_case, exc_info))
            # explicitly break a reference cycle:
            # exc_info -> frame -> exc_info
            exc_info = None
        else:
            if self.result_supports_subtests and self.success:
                self.errors.append((test_case, None))
        finally:
            self.success = self.success and old_success