Changes between Version 15 and Version 16 of Python

Timestamp:

02/02/09 13:36:47 (16 years ago)

Author:

atzm

Comment:

--

Python

@@ -43 +43 @@
 1 2 3
 }}}
+
+== hidden read-ahead buffer ==
+ * [http://docs.python.org/library/stdtypes.html#file.next Built-in Types -- Python v2.6.1 documentation (#file.next)] より
+{{{
+In order to make a for loop the most efficient way of looping
+over the lines of a file (a very common operation),
+the next() method uses a hidden read-ahead buffer.
+}}}
+
+ * next() を見る
+   * コード
+{{{
+#!python
+def printrss():
+    pf = open('/proc/self/status')
+    for l in pf:
+        if l[:5] == 'VmRSS':
+            print l,
+    pf.close()
+
+def test(fname='/path/to/huge_file'):
+    f = open(fname)
+    c = 1
+    for i in f:
+        print '===== %d =====' % c
+        printrss()
+        c += 1
+    f.close()
+
+print 'test1'
+test()
+}}}
+   * 結果
+{{{
+  :     :     :
+===== 1 =====
+VmRSS:      2392 kB
+  :     :     :
+===== 11212 =====
+VmRSS:      2408 kB
+}}}
+     * ちょっと (16KB) だけ増えてる
+
+ * readline() を見る
+   * コード
+{{{
+#!python
+def printrss():
+    pf = open('/proc/self/status')
+    for l in pf:
+        if l[:5] == 'VmRSS':
+            print l,
+    pf.close()
+
+def test(fname='/path/to/huge_file'):
+    f = open(fname)
+    c = 1
+    while True:
+        i = f.readline()
+        if not i: break
+        print '===== %d =====' % c
+        printrss()
+        c += 1
+    f.close()
+
+print 'test1'
+test()
+}}}
+   * 結果
+{{{
+  :     :     :
+===== 1 =====
+VmRSS:      2396 kB
+  :     :     :
+===== 11212 =====
+VmRSS:      2396 kB
+}}}
+     * 増えてない
 
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