5.8 starting...

cookbook/c05/p08_iterate_fixedsize.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+# -*- encoding: utf-8 -*-
+"""
+Topic: 固定长度迭代文件
+Desc : 
+"""
+from functools import partial
+
+
+def iterate_fixed():
+    RECORD_SIZE = 32
+
+    with open('somefile.data', 'rb') as f:
+        records = iter(partial(f.read, RECORD_SIZE), b'')
+        for r in records:
+            print(r)
+
+if __name__ == '__main__':
+    iterate_fixed()
+

source/c05/p08_iterate_over_fixed_sized_records.rst

@@ -5,14 +5,43 @@
 ----------
 问题
 ----------
-todo...
+你想在一个固定长度记录或者数据块的集合上迭代，而不是在一个文件中一行一行的迭代。
+
+|
 
 ----------
 解决方案
 ----------
-todo...
+通过下面这个小技巧使用 ``iter`` 和 ``functools.partial()`` 函数：
+
+.. code-block:: python
+
+    from functools import partial
+
+    RECORD_SIZE = 32
+
+    with open('somefile.data', 'rb') as f:
+        records = iter(partial(f.read, RECORD_SIZE), b'')
+        for r in records:
+            ...
+
+这个例子中的 ``records`` 对象是一个可迭代对象，它会不断的产生固定大小的数据块，直到文件末尾。
+要注意的是如果总记录大小不是块大小的整数倍的话，最后一个返回元素的字节数会比期望值少。
+
+|
 
 ----------
 讨论
 ----------
-todo...
+A little-known feature of the iter() function is that it can create an iterator if you pass
+it a callable and a sentinel value. The resulting iterator simply calls the supplied callable
+over and over again until it returns the sentinel, at which point iteration stops.
+
+In the solution, the functools.partial is used to create a callable that reads a fixed
+number of bytes from a file each time it’s called. The sentinel of b'' is what gets returned
+when a file is read but the end of file has been reached.
+
+Last, but not least, the solution shows the file being opened in binary mode. For reading
+fixed-sized records, this would probably be the most common case. For text files, reading
+line by line (the default iteration behavior) is more common.
+