pyt...@bdurham.com wrote:
> My understanding is that appending to a list and then joining
> this list when done is the fastest technique for string
> concatenation. Is this true?
>
> The 3 string concatenation techniques I can think of are:
>
> - append to list, join
> - string 'addition' (s = s + char)
> - cStringIO
>
> The code that follows my signature confirms that the list
> append/join technique is indeed the fastest of these 3
> approaches, but perhaps there are other techniques I should
> consider?
>
> Malcolm
>
> # test various techniques for string concatenation
> import cStringIO
> import timeit
> source = 'x' * 5000000
> def testListAppend():
> output = list()
> for char in source:
> output.append( char )
> output = ''.join( output )
You are measuring list creation here, not string concatenation:
$ python -m timeit -s's = "x"*10**5' 'd = []' 'for c in s: d.append(c)'
10 loops, best of 3: 20.9 msec per loop
$ python -m timeit -s's = ["x"]*10**5' '"".join(s)'
100 loops, best of 3: 2.47 msec per loop
To fix that I'd start with a list, not a string:
source = ["x"] * 5000000
> def testStringIO():
> output = cStringIO.StringIO()
> for char in source:
> output.write( char )
> output = output.getvalue()
You can simplify that to
def test_stringio():
output = cStringIO.StringIO()
output.writelines(source) # doesn't add newlines
output = output.getvalue()
which is almost as fast as ''.join:
$ python -m timeit -s's = ["x"]*10**5' '"".join(s)'
100 loops, best of 3: 2.47 msec per loop
$ python -m timeit -s's = ["x"]*10**5' -s 'from cStringIO import StringIO'
'o = StringIO(); o.writelines(s); o.getvalue()'
100 loops, best of 3: 2.88 msec per loop
Peter
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