*groan* I did the equivalent of: a = "blah de BLAH" b = "%s" % a a is b => False a == b => True
It makes a deepcopy or a double reference for all I know. Even two equal immutable strings fail the "is" test, so I stand by my statement that "is" is bad form unless you are working with an object that is mutable. I hope it's not making a double reference, that would be bad design. I apologize for glossing over your explicit statement that str are immutable. Indeed. I could have reduced my emails by [4,3]. On Aug 2, 1:22 pm, mda_ <donmorri...@gmail.com> wrote: > Another Caveat: str doesn't implement .__copy__ or .__deepcopy__ so > I'm being silly....but the main point being "is" is object comparison > not equality. Ok, email on exponential backoff!! ;-) > > On Aug 2, 11:06 am, mda_ <donmorri...@gmail.com> wrote: > > > > > Caveat: Hopefully my chaining of operators there didn't mislead, that > > was unintended. I think most of what I said still holds, if not all. > > > -Don > > > On Aug 2, 9:14 am, mda_ <donmorri...@gmail.com> wrote: > > > > SageDevs, > > > > In the interest of "gotchas", please consider the following: > > > > The built-in str, and the module string are different, though both > > > return type str according to type(). > > > > Example: > > > > d...@dv9000-laptop:~$ python2.6 > > > Python 2.6.4 (r264:75706, Dec 7 2009, 18:43:55) > > > [GCC 4.4.1] on linux2 > > > Type "help", "copyright", "credits" or "license" for more information.>>> > > > from copy import copy,deepcopy > > > >>> import string > > > >>> a = '12 3 four five six' > > > >>> a is copy(a) is deepcopy(a) > > > True > > > >>> a == copy(a) == deepcopy(a) > > > True > > > >>> b = string.lower(a) > > > >>> a > > > > '12 3 four five six' > > > > >>> a is b > > > False > > > >>> a == b > > > True > > > >>> type(a) > > > <type 'str'> > > > >>> type(b) > > > <type 'str'> > > > >>> c = copy(a) > > > >>> c is a > > > True > > > >>> d = deepcopy(a) > > > >>> d is a > > > True > > > >>> hash(a) == hash(b) > > > True > > > >>> id(a) == id(b) > > > False > > > >>> id(a) == id(c) == id(d) > > > True > > > >>> id(a) is id(c) is id(d) > > > False > > > >>> hash(a) == hash(b) == hash(c) == hash(d) > > > True > > > >>> hash(a) is hash(b) is hash(c) is hash(d) > > > False > > > >>> type(a) == type(b) == type(c) == type(d) > > > True > > > >>> type(a) is type(b) is type(c) is type(d) > > > True > > > > So, I think the take home message is that the keyword "is" is fragile > > > in some cases. Also, the return value of type() is misleading. > > > >http://docs.python.org/release/2.6.5/reference/lexical_analysis.html#... > > > > Cheers, > > > Don -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
