[issue41242] When concating strings, I think it is better to use += than join the list

[Rémi Lapeyre]

Rémi Lapeyre <remi.lapeyre at henki.fr> added the comment:

Hi Wansoo, using += instead of str.join() is less performant. Concatenating n strings with + will create and allocate n new strings will str.join() will carefully look ahead and allocate the correct amount of memory and do all concatenation at one:


➜  ~ python3 -m timeit -s 's = ""' 'for i in range(1_000_000): s += "foo\n"'
5 loops, best of 5: 107 msec per loop
➜  ~ python3 -m timeit -s 'l = ["foo"]*1_000_000' '"\n".join(l)'
20 loops, best of 5: 9.96 msec per loop


It's a common idiom that you will meet a lot in Python.

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nosy: +remi.lapeyre

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