Counter to the PythonSpeed/PerformanceTips, on python 2.4 the following string concatenation is almost twice as fast:
as:
On the win32 Python 2.4 I'm seeing the join sample above complete in less than half the time of the concatenating sample.
- -db
Usually the join() is located outside the loop, that code makes this extremely hard though (becuase of the self-referencing of the generated string). But that situation is not the norm. -- JürgenHermann 2005-08-01 06:07:51
Are you guys kidding? The whole page is contrieved. Correct implementation of "join" is:
from time import time
t = time()
s = 'lksdajflakjdsflku09uweoir'
r = [s]
for x in range(40):
r.append(s[len(s)/2:])
s = "".join(r)
print 'duration:', time()-twhich gives on PythonWin 2.4 (#60, Nov 30 2004, 09:34:21) [MSC v.1310 32 bit (Intel)] on win32 execution times:
1st duration: 54.4060001373 Last duration: 0.0160000324249
-- -- MikeRovner 2005-08-02 10:19:06
Mike, that code generates a very different (and much shorter) s. Note how the original code takes the half of the preconcatenated s, making the size grow exponentially (which generates megabytes of data). -- JürgenHermann 2005-08-30 18:44:05
-- -- DavidFord 2005-10-18 10:19:06 A few notes (your mileage may vary - this is a 4Mb file being stripped of unprintable characters)
- Regex replacement rather than creating a list and joining it is 2.5x faster than the tooling above
This is far slower than the equivalent Java code (around 4x slower) using String.charAt() and StringBuffers
I tend to create a stream of strings in a loop that should be concatenated. I generated the script to test the join vs += performance for some randomly generated data and found that for 100,000 strings of length up to ten characters, join is maybe 20% faster than using +=. It certainly was not an order of magnitude faster. The results tended to vary each time through the outer loop, even though I attempted to control the garbage collection and ensured my Windows XP machine was 95% idle apart from running the script.