From: Andrew Dalke <dalke@dalkescientific.com>
Date: Fri, 26 May 2006 22:49:03 +0000 (+0000)
Subject: Added description of why splitlines doesn't use the prealloc strategy
X-Git-Tag: v2.5b1~422
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=7e0a62ea9052faf0e19dc2438124751b8f68ce16;p=thirdparty%2FPython%2Fcpython.git

Added description of why splitlines doesn't use the prealloc strategy
---

diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index c59c74ed05e9..7e9378394b9c 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -3768,6 +3768,14 @@ string_splitlines(PyStringObject *self, PyObject *args)
     data = PyString_AS_STRING(self);
     len = PyString_GET_SIZE(self);
 
+    /* This does not use the preallocated list because splitlines is
+       usually run with hundreds of newlines.  The overhead of
+       switching between PyList_SET_ITEM and append causes about a
+       2-3% slowdown for that common case.  A smarter implementation
+       could move the if check out, so the SET_ITEMs are done first
+       and the appends only done when the prealloc buffer is full.
+       That's too much work for little gain.*/
+
     list = PyList_New(0);
     if (!list)
         goto onError;