From afff86f0a6f8224a2bd0ec6c299115cb09dd04d0 Mon Sep 17 00:00:00 2001
From: XiongNeng <yidao620@gmail.com>
Date: Mon, 1 Sep 2014 01:13:58 +0800
Subject: [PATCH] =?UTF-8?q?1.3=E8=8A=82=E7=BF=BB=E8=AF=91=E5=AE=8C?=
 =?UTF-8?q?=E6=88=90?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 cookbook/c01/p03_nitem.py            | 27 ++++++++++
 cookbook/somefile.txt                | 19 +++++++
 source/c01/p03_keep_last_n_items.rst | 80 ++++++++++++++++++++++++++--
 3 files changed, 123 insertions(+), 3 deletions(-)
 create mode 100644 cookbook/c01/p03_nitem.py
 create mode 100644 cookbook/somefile.txt

diff --git a/cookbook/c01/p03_nitem.py b/cookbook/c01/p03_nitem.py
new file mode 100644
index 0000000..0a857f3
--- /dev/null
+++ b/cookbook/c01/p03_nitem.py
@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+# -*- encoding: utf-8 -*-
+"""
+Topic: collections.deque演示
+Desc : deque有一个maxlen参数，当append的时候，如果超过，那么最前面的就被挤出队列。
+"""
+from collections import deque
+
+
+def search(lines, pattern, history=5):
+    previous_lines = deque(maxlen=history)
+    for li in lines:
+        if pattern in li:
+            yield li, previous_lines
+        previous_lines.append(li)
+
+# Example use on a file
+if __name__ == '__main__':
+    with open(r'../../cookbook/somefile.txt') as f:
+        for line, prevlines in search(f, 'Python', 5):
+            for pline in prevlines:
+                print(pline, end='')
+            print(line, end='')
+            print('-' * 20)
+
+
+
diff --git a/cookbook/somefile.txt b/cookbook/somefile.txt
new file mode 100644
index 0000000..243b7c4
--- /dev/null
+++ b/cookbook/somefile.txt
@@ -0,0 +1,19 @@
+Python is powerful... and fast;
+plays well with others;
+runs everywhere;
+is friendly & easy to learn;
+is Open.
+These are some of the reasons people who use Python would rather not use anything else.
+
+Python can be easy to pick up whether you're a first time programmer
+or you're experienced with other languages.
+The following pages are a useful first step to get on your way
+writing programs with Python!
+
+The community hosts conferences and meetups, collaborates on code,
+and much more. Python's documentation will help you along the way,
+and the mailing lists will keep you in touch.
+
+Conferences and Workshops
+Python Documentation
+Mailing Lists and IRC channels
\ No newline at end of file
diff --git a/source/c01/p03_keep_last_n_items.rst b/source/c01/p03_keep_last_n_items.rst
index bad49b1..5e46259 100644
--- a/source/c01/p03_keep_last_n_items.rst
+++ b/source/c01/p03_keep_last_n_items.rst
@@ -5,14 +5,88 @@
 ----------
 问题
 ----------
-todo...
+在迭代操作或者其他操作的时候，你只想保留最后有限几个元素的历史记录。
 
 ----------
 解决方案
 ----------
-todo...
+保留有限历史记录正是collections.deque大显身手的时候。比如，下面的代码在多行上面做简单的文本匹配，
+并只返回在前N行中匹配成功的行：
+
+.. code-block:: python
+
+    from collections import deque
+
+
+    def search(lines, pattern, history=5):
+        previous_lines = deque(maxlen=history)
+        for li in lines:
+            if pattern in li:
+                yield li, previous_lines
+            previous_lines.append(line)
+
+    # Example use on a file
+    if __name__ == '__main__':
+        with open(r'../../cookbook/somefile.txt') as f:
+            for line, prevlines in search(f, 'Python', 5):
+                for pline in prevlines:
+                    print(pline, end='')
+                print(line, end='')
+                print('-' * 20)
 
 ----------
 讨论
 ----------
-todo...
+我们在写查询元素的代码的时候，通常会使用包含yield表达式的生成器函数，也就是我们上面示例代码中的那样。
+这样可以将搜索过程代码和使用搜索结果代码解耦。如果你还不清楚什么是生成器，请参看4.3节。
+
+Using deque(maxlen=N) creates a fixed-sized queue. When new items are added and
+the queue is full, the oldest item is automatically removed. For example:
+使用deque(maxlen=N)构造函数会新建一个固定大小的队列。当心的元素加入并且这个队列已满的时候，
+最老的元素会自动被移除掉。
+
+代码示例：
+
+.. code-block:: python
+
+    >>> q = deque(maxlen=3)
+    >>> q.append(1)
+    >>> q.append(2)
+    >>> q.append(3)
+    >>> q
+    deque([1, 2, 3], maxlen=3)
+    >>> q.append(4)
+    >>> q
+    deque([2, 3, 4], maxlen=3)
+    >>> q.append(5)
+    >>> q
+    deque([3, 4, 5], maxlen=3)
+
+尽管你也可以手动在一个列表上实现这一的操作(比如增加、删除等等)。
+但是这里的队列方案会更加优雅并且运行得更快些。
+
+更一般的，deque类可以被用在任何你只需要一个简单队列数据结构的场合。
+如果你不设置最大队列大小，那么就会得到一个无限大小队列，你可以在队列的两端执行添加和弹出元素的操作。
+
+代码示例：
+
+.. code-block:: python
+
+    >>> q = deque()
+    >>> q.append(1)
+    >>> q.append(2)
+    >>> q.append(3)
+    >>> q
+    deque([1, 2, 3])
+    >>> q.appendleft(4)
+    >>> q
+    deque([4, 1, 2, 3])
+    >>> q.pop()
+    3
+    >>> q
+    deque([4, 1, 2])
+    >>> q.popleft()
+    4
+
+在队列两端添加或删除元素时间复杂度都是O(1)，而在list的开头插入或删除元素的时间复杂度为O(N)。
+