Re: [Jython-dev] string concatination performance

[Bryn K. <xo...@xo...>]

Daniel Rall wrote:

>"Moyer, Todd" <TMoyer@TALK.COM> writes:
>
>  
>
>>I came across the following dramatic performance improvement in my code and
>>thought I'd pass it along.  I know Jython isn't choosen for it's blinding
>>speed, but in this case my response time went from painful to trivial.  I
>>did a quick search of the archives and the web in general and didn't see any
>>discussion of this.  Apologies if it's widely known.
>>
>>I was putting together a string representation of a Table object I
>>developed.  One of my most common uses for this is taking the output of an
>>SQL select, which can get quite large.  I had been doing a lot of string
>>concatination (string = string + "foo").  Needless to say, this got really
>>slow when the tables were big:  5,000 rows was taking almost a minute.  I
>>reimplemented using the Java StringBuffer's "append" method.  Execution time
>>dropped to about 1 second.
>>
>>Using the Java object in my Jython code was easy; I can post it if anyone
>>wants to see it.  However, is there pure Jython way to do this that I'm
>>overlooking?  If not, is this something worth adding to the language?
>>    
>>
>
>When not in a loop or conditional, most Java compilers do this for you
>now a days.  Not knowing anything about the internals of Jython, I
>wonder if a Python str/StringType might be better represented
>internally using a StringBuffer in Jython.
>
Concatenating strings is a slow way of doing things in most languages,
it's almost always better to use a StringBuffer or a list or something
like that to collect the pieces, and make them into a string at the end.
Here's a pure {P,J}ython solution that shows a big difference without
having to import Java classes:

import time
LOOPSIZE = 20000

def slowway():
    start = time.time()
    foo = ""
    for i in xrange(LOOPSIZE):
        foo = foo + "foo"
    final = foo
    print "Time:", time.time() - start

def fastway():
    start = time.time()
    foo = []
    for i in xrange(LOOPSIZE):
        foo.append("foo")
    final = "".join(foo)
    print "Time:", time.time() - start

#First do it the slow way (string concatentation)
slowway()

#Then with the fast way (Joining a list of strings together)
fastway()

Running this script under Jython 2.1 prints:

Time: 7.0
Time: 0.09100008010864258

Regards,
Bryn