[Python-Dev] New stringbench benchmark results

[Steven D'Aprano]

Victor Stinner wrote:
> Hum, copy-paste failure, I wrote numbers in the wrong order, it's:
> 
> (test: Python 3.2 => Python 3.3)
> "A".join(["Bob"]*100)): 0.92 => 2.11
> ("C"+"AB"*300).rfind("CA"): 0.57 => 1.03
> ("A" + ("Z"*128*1024)).replace("A", "BB", 1): 0.25 => 0.50
> 
> I improved str.replace(): it's now 5 times faster instead of 2 times slower 
> for this specific benchmark :-) (or 10 times faster in Python 3.3 before/after 
> my patch)


Talking about str.replace, I was surprised to see this behaviour in 3.2:

 >>> s = 'spam'
 >>> t = s.replace('a', 'a')
 >>> s is t
False

Given that strings are immutable, would it not be an obvious 
optimization for replace to return the source string unchanged if the 
old and new substrings are equal, and avoid making a potentially 
expensive copy?

I note that if count is zero, the source string is returned unchanged:

 >>> t = s.replace('a', 'b', 0)
 >>> t is s
True


-- 
Steven