9.5小节完成~

Author: yidao620c

cookbook/c09/p03_unwrap_decorator.py

@@ -7,20 +7,23 @@
 
 from functools import wraps
 
+
 def decorator1(func):
     @wraps(func)
     def wrapper(*args, **kwargs):
         print('Decorator 1')
         return func(*args, **kwargs)
     return wrapper
 
+
 def decorator2(func):
     @wraps(func)
     def wrapper(*args, **kwargs):
         print('Decorator 2')
         return func(*args, **kwargs)
     return wrapper
 
+
 @decorator1
 @decorator2
 def add(x, y):

cookbook/c09/p05_adjust_attribute.py

@@ -0,0 +1,118 @@
+#!/usr/bin/env python
+# -*- encoding: utf-8 -*-
+"""
+Topic: 可调整属性的装饰器
+Desc : 
+"""
+
+from functools import wraps, partial
+import logging
+import time
+
+
+# Utility decorator to attach a function as an attribute of obj
+def attach_wrapper(obj, func=None):
+    if func is None:
+        return partial(attach_wrapper, obj)
+    setattr(obj, func.__name__, func)
+    # return func
+
+
+def logged(level, name=None, message=None):
+    """
+    Add logging to a function. level is the logging
+    level, name is the logger name, and message is the
+    log message. If name and message aren't specified,
+    they default to the function's module and name.
+    """
+
+    def decorate(func):
+        logname = name if name else func.__module__
+        log = logging.getLogger(logname)
+        logmsg = message if message else func.__name__
+
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            log.log(level, logmsg)
+            return func(*args, **kwargs)
+
+        # Attach setter functions
+        @attach_wrapper(wrapper)
+        def set_level(newlevel):
+            nonlocal level
+            level = newlevel
+
+        @attach_wrapper(wrapper)
+        def set_message(newmsg):
+            nonlocal logmsg
+            logmsg = newmsg
+
+        return wrapper
+
+    return decorate
+
+
+# Example use
+@logged(logging.DEBUG)
+def add(x, y):
+    return x + y
+
+
+@logged(logging.CRITICAL, 'example')
+def spam():
+    print('Spam!')
+
+
+logging.basicConfig(level=logging.DEBUG)
+add(2, 3)
+add.set_message('Add called')
+add(2, 3)
+add.set_level(logging.WARNING)
+add(2, 3)
+
+print('---------------------')
+spam()
+spam.set_message('Add called')
+spam()
+spam.set_level(logging.WARNING)
+spam()
+
+
+def timethis(func):
+    """
+    Decorator that reports the execution time.
+    """
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        start = time.time()
+        result = func(*args, **kwargs)
+        end = time.time()
+        print(func.__name__, end - start)
+        return result
+
+    return wrapper
+
+
+@logged(logging.DEBUG)
+@timethis
+def countdown(n):
+    while n > 0:
+        n -= 1
+
+countdown(10000000)
+countdown.set_level(logging.WARNING)
+countdown.set_message("Counting down to zero")
+countdown(10000000)
+
+
+@timethis
+@logged(logging.DEBUG)
+def countdown1(n):
+    while n > 0:
+        n -= 1
+
+print('****************************************')
+countdown1(10000000)
+countdown1.set_level(logging.WARNING)
+countdown1.set_message("Counting down to zero")
+countdown1(10000000)

source/c09/p05_define_decorator_with_user_adjustable_attributes.rst

@@ -1,18 +1,164 @@
 ============================
-9.5 定义用户可调整属性的装饰器
+9.5 可自定义属性的装饰器
 ============================
 
 ----------
 问题
 ----------
-todo...
+你想写一个装饰器来包装一个函数，并且允许用户提供参数在运行时控制装饰器行为。
+
+|
 
 ----------
 解决方案
 ----------
-todo...
+引入一个访问函数，使用 ``nolocal`` 来修改内部变量。
+然后这个访问函数被作为一个属性赋值给包装函数。
+
+.. code-block:: python
+
+    from functools import wraps, partial
+    import logging
+    # Utility decorator to attach a function as an attribute of obj
+    def attach_wrapper(obj, func=None):
+        if func is None:
+            return partial(attach_wrapper, obj)
+        setattr(obj, func.__name__, func)
+        return func
+
+    def logged(level, name=None, message=None):
+        '''
+        Add logging to a function. level is the logging
+        level, name is the logger name, and message is the
+        log message. If name and message aren't specified,
+        they default to the function's module and name.
+        '''
+        def decorate(func):
+            logname = name if name else func.__module__
+            log = logging.getLogger(logname)
+            logmsg = message if message else func.__name__
+
+            @wraps(func)
+            def wrapper(*args, **kwargs):
+                log.log(level, logmsg)
+                return func(*args, **kwargs)
+
+            # Attach setter functions
+            @attach_wrapper(wrapper)
+            def set_level(newlevel):
+                nonlocal level
+                level = newlevel
+
+            @attach_wrapper(wrapper)
+            def set_message(newmsg):
+                nonlocal logmsg
+                logmsg = newmsg
+
+            return wrapper
+
+        return decorate
+
+    # Example use
+    @logged(logging.DEBUG)
+    def add(x, y):
+        return x + y
+
+    @logged(logging.CRITICAL, 'example')
+    def spam():
+        print('Spam!')
+
+下面是交互环境下的使用例子：
+
+.. code-block:: python
+
+    >>> import logging
+    >>> logging.basicConfig(level=logging.DEBUG)
+    >>> add(2, 3)
+    DEBUG:__main__:add
+    5
+    >>> # Change the log message
+    >>> add.set_message('Add called')
+    >>> add(2, 3)
+    DEBUG:__main__:Add called
+    5
+    >>> # Change the log level
+    >>> add.set_level(logging.WARNING)
+    >>> add(2, 3)
+    WARNING:__main__:Add called
+    5
+    >>>
+
+|
 
 ----------
 讨论
 ----------
-todo...
+这一小节的关键点在于访问函数(如 ``set_message()`` 和 ``set_level()`` )，它们被作为属性赋给包装器。
+每个访问函数允许使用 ``nonlocal`` 来修改函数内部的变量。
+
+还有一个令人吃惊的地方是访问函数会在多层装饰器间传播(如果你的装饰器都使用了 ``@functools.wraps`` 注解)。
+例如，假设你引入另外一个装饰器，比如9.2小节中的 ``@timethis`` ，像下面这样：
+
+.. code-block:: python
+
+    @timethis
+    @logged(logging.DEBUG)
+    def countdown(n):
+        while n > 0:
+            n -= 1
+
+你会发现访问函数依旧有效：
+
+.. code-block:: python
+
+    >>> countdown(10000000)
+    DEBUG:__main__:countdown
+    countdown 0.8198461532592773
+    >>> countdown.set_level(logging.WARNING)
+    >>> countdown.set_message("Counting down to zero")
+    >>> countdown(10000000)
+    WARNING:__main__:Counting down to zero
+    countdown 0.8225970268249512
+    >>>
+
+你还会发现即使装饰器像下面这样以相反的方向排放，效果也是一样的：
+
+.. code-block:: python
+
+    @logged(logging.DEBUG)
+    @timethis
+    def countdown(n):
+        while n > 0:
+            n -= 1
+
+还能通过使用lambda表达式代码来让访问函数的返回不同的设定值：
+
+.. code-block:: python
+
+    @attach_wrapper(wrapper)
+    def get_level():
+        return level
+
+    # Alternative
+    wrapper.get_level = lambda: level
+
+一个比较难理解的地方就是对于访问函数的首次使用。例如，你可能会考虑另外一个方法直接访问函数的属性，如下：
+
+.. code-block:: python
+
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        wrapper.log.log(wrapper.level, wrapper.logmsg)
+        return func(*args, **kwargs)
+
+    # Attach adjustable attributes
+    wrapper.level = level
+    wrapper.logmsg = logmsg
+    wrapper.log = log
+
+这个方法也可能正常工作，但前提是它必须是最外层的装饰器才行。
+如果它的上面还有另外的装饰器(比如上面提到的 ``@timethis`` 例子)，那么它会隐藏底层属性，使得修改它们没有任何作用。
+而通过使用访问函数就能避免这样的局限性。
+
+最后提一点，这一小节的方案也可以作为9.9小节中装饰器类的另一种实现方法。
+