On 21 April 2018 at 11:42, Chris Angelico <ros...@gmail.com> wrote: > On Sat, Apr 21, 2018 at 8:25 PM, Yinbin Ma <mayinbin...@gmail.com> wrote: >> Hi all: >> >> I notice that if concatenating two stringobjects, PVM will not check the >> dictionary of interned string. For example: >> >>>>> a = "qwerty" >>>>> b = "qwe" >>>>> c = "rty" >>>>> d = b+c >>>>> id(a) >> 4572089736 >>>>> id(d) >> 4572111176 >>>>> e = "".join(["qwe","rty"]) >>>>> id(e) >> 4546460280 >> >> But if concatenating two string directly, PVM would check the dictionary: >> >>>>> a = "qwerty" >>>>> b = "qwe"+"rty" >>>>> id(a) >> 4546460112 >>>>> id(b) >> 4546460112 >> >> It happens in Py2 and Py3 both. >> Is it necessary for fixing this bug or not? >> > > What you're seeing there is actually the peephole optimizer at work. > Your assignment to 'b' here is actually the exact same thing as 'a', > by the time you get to execution. If you're curious about what's > happening, check out the dis.dis() function and have fun! :)
To clarify, though, this is not a bug. The language doesn't guarantee that the two strings will have the same id, just that they will be equal (in the sense of ==). Paul _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
