file.writelines( seq ) and map( file.write, seq ) are the same; the former is syntactic sugar for the later.
Well, that's not exactly true. For one thing, map(file.write, seq) returns a list of Nones, while file.writelines returns only the single None that Python functions with no return statement do. More substantially, file.writelines (as far as I can tell from the C code) doesn't make any call to file.write.
I looked at fileobject.c and it looks like file.writelines makes a call to 'fwrite' for each item in the iterable given. Your code, if I read it right, makes a call to 'writev' for each item in the iterable.
I looked at the fwrite() and writev() docs and read your comments, but I still couldn't quite figure out what makes 'writev' more efficient than 'fwrite' for the same size buffer... Mind trying to explain it to me again?
There is one more time that writev would be beneficial ... perhaps you
want to write a never ending sequence with a minimum of overhead?
def camera(): while 1: yield extract_entropy( grab_frame() )
open( "/tmp/entropy_daemon_pipe", "w+" ).writev( camera(), 5 )
I tried running:
py> def gen():
... i = 1
... while True:
... yield '%i\n' % i
... i *= 10
...
py> open('integers.txt', 'w').writelines(gen())and, while (of course) it runs forever, I don't appear to get any memory problems. I seem to be able to write fairly large integers too:
$ tail -n 1 integers.txt | wc
1 1 5001How big do the items in the iterable need to be for writev to be necessary?
Steve
P.S. I certainly don't have anything against including your patch (not that my opinion counts for anything) ;) but if it improves a common file.writelines usage, I'd like to see it used there too when possible.
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