From a25c4c09add49ff869e1f473c99a50d87a31e9dc Mon Sep 17 00:00:00 2001
From: XiongNeng <yidao620@gmail.com>
Date: Thu, 5 Feb 2015 16:14:15 +0800
Subject: [PATCH] =?UTF-8?q?8.20=E5=B0=8F=E8=8A=82=E5=AE=8C=E6=88=90?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 basic/mystring/strformat.py                   |  4 +-
 cookbook/c08/p20_invoke_bystr.py              | 40 +++++++++++
 ...0_call_method_on_object_by_string_name.rst | 68 ++++++++++++++++++-
 3 files changed, 108 insertions(+), 4 deletions(-)
 create mode 100644 cookbook/c08/p20_invoke_bystr.py

diff --git a/basic/mystring/strformat.py b/basic/mystring/strformat.py
index 5342d4b..22685b6 100644
--- a/basic/mystring/strformat.py
+++ b/basic/mystring/strformat.py
@@ -7,6 +7,7 @@
 
 __author__ = 'Xiong Neng'
 
+
 def simple():
     # 一般的%形式的格式化
     a = 42
@@ -33,7 +34,8 @@ def simple():
     name = 'Elwood'
     age = 99
     print('%(name)s is %(age)s years old.' % vars())
-    #print('{0} {1} {2}'.format())
+    # print('{0} {1} {2}'.format())
+
 
 def senior():
     """高级字符串格式化"""
diff --git a/cookbook/c08/p20_invoke_bystr.py b/cookbook/c08/p20_invoke_bystr.py
new file mode 100644
index 0000000..29c54fb
--- /dev/null
+++ b/cookbook/c08/p20_invoke_bystr.py
@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+# -*- encoding: utf-8 -*-
+"""
+Topic: 通过字符串调用方法
+Desc : 
+"""
+
+import math
+
+
+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+    def __repr__(self):
+        # !r表示调用后面参数的__repr__()方法
+        return 'Point({!r:},{!r:})'.format(self.x, self.y)
+
+    def distance(self, x, y):
+        return math.hypot(self.x - x, self.y - y)
+
+
+p = Point(2, 3)
+d = getattr(p, 'distance')(0, 0)  # Calls p.distance(0, 0)
+
+import operator
+
+operator.methodcaller('distance', 0, 0)(p)
+
+points = [
+    Point(1, 2),
+    Point(3, 0),
+    Point(10, -3),
+    Point(-5, -7),
+    Point(-1, 8),
+    Point(3, 2)
+]
+# Sort by distance from origin (0, 0)
+points.sort(key=operator.methodcaller('distance', 0, 0))
diff --git a/source/c08/p20_call_method_on_object_by_string_name.rst b/source/c08/p20_call_method_on_object_by_string_name.rst
index 15aeff0..314a0fd 100644
--- a/source/c08/p20_call_method_on_object_by_string_name.rst
+++ b/source/c08/p20_call_method_on_object_by_string_name.rst
@@ -5,14 +5,76 @@
 ----------
 问题
 ----------
-todo...
+你有一个字符串形式的方法名称，想通过它调用某个对象的对应方法。
+
+|
 
 ----------
 解决方案
 ----------
-todo...
+最简单的情况，可以使用 ``getattr()`` ：
+
+.. code-block:: python
+
+    import math
+
+    class Point:
+        def __init__(self, x, y):
+            self.x = x
+            self.y = y
+
+        def __repr__(self):
+            return 'Point({!r:},{!r:})'.format(self.x, self.y)
+
+        def distance(self, x, y):
+            return math.hypot(self.x - x, self.y - y)
+
+
+    p = Point(2, 3)
+    d = getattr(p, 'distance')(0, 0)  # Calls p.distance(0, 0)
+
+另外一种方法是使用 ``operator.methodcaller()`` ，例如：
+
+.. code-block:: python
+
+    import operator
+    operator.methodcaller('distance', 0, 0)(p)
+
+当你需要通过相同的参数多次调用某个方法时，使用 ``operator.methodcaller`` 就很方便了。
+比如你需要排序一系列的点，就可以这样做：
+
+.. code-block:: python
+
+    points = [
+        Point(1, 2),
+        Point(3, 0),
+        Point(10, -3),
+        Point(-5, -7),
+        Point(-1, 8),
+        Point(3, 2)
+    ]
+    # Sort by distance from origin (0, 0)
+    points.sort(key=operator.methodcaller('distance', 0, 0))
+
+|
 
 ----------
 讨论
 ----------
-todo...
\ No newline at end of file
+调用一个方法实际上是两部独立操作，第一步是查找属性，第二步是函数调用。
+因此，为了调用某个方法，你可以首先通过 ``getattr()`` 来查找到这个属性，然后再去以函数方式调用它即可。
+
+``operator.methodcaller()`` 创建一个可调用对象，并同时提供所有必要参数，
+然后调用的时候只需要将实例对象传递给它即可，比如：
+
+.. code-block:: python
+
+    >>> p = Point(3, 4)
+    >>> d = operator.methodcaller('distance', 0, 0)
+    >>> d(p)
+    5.0
+    >>>
+
+通过方法名称字符串来调用方法通常出现在需要模拟 ``case`` 语句或实现访问者模式的时候。
+参考下一小节获取更多高级例子。
+