A small test revealed that "".join(listOfStrings) is
not faster than plain +=. The .join() is slower. Using .append() and .join() is slower.
real 0m2.908sTime with +=:
real 0m1.742sThe test:
#!/usr/bin/env python
def combine(inc, count):
text = ""
for i in xrange(count):
text += inc
return len(text)
def combineByJoin(inc, count):
text = []
for i in xrange(count):
text.append(inc)
text = "".join(text)
return len(text)
def main():
inc = "a" * 10
print combine(inc, 10000000)
#print combineByJoin(inc, 10000000)
main()
Tested on Python 2.5.2.
Posts
2 comments:
This is not a fair comparison as you are building up a list before you combine by joining. Just comparing concatenation vs. joining yields different results:
In [20]: text=""
In [21]: a=['aaaaa']*1000000
In [22]: %time for c in a: text+=c
CPU times: user 0.67 s, sys: 0.03 s, total: 0.70 s
Wall time: 0.71 s
In [24]: %time text="".join(a)
CPU times: user 0.10 s, sys: 0.01 s, total: 0.10 s
Wall time: 0.10 s
Yes you are right. I should not write that join() is slower.
A more correct statement would be:
Using .append() followed by .join() is slower than using += directly.
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