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From: "Prasad, Ramit" <ramit.prasad@jpmorgan.com>
To: Roy Smith <roy@panix.com>, "python-list@python.org" <python-list@python.org>
Subject: RE: Python Interview Questions
Thread-Topic: Python Interview Questions
Thread-Index: AQHNxmZzpYQlLxpYg0GWQxx92IFaPpfxwynQ
Date: Mon, 19 Nov 2012 23:57:43 +0000
References: <1193768041.349129.26350@v3g2000hsg.googlegroups.com> <55443eb7-847c-4f4c-8d04-1e6b507aac00@googlegroups.com> <50a8acdc$0$29978$c3e8da3$5496439d@news.astraweb.com> <roy-EFE1F1.08532518112012@news.panix.com> <50a911ec$0$29978$c3e8da3$5496439d@news.astraweb.com> <roy-B2D5FF.12535018112012@news.panix.com> <50a97de0$0$29983$c3e8da3$5496439d@news.astraweb.com> <roy-BD53B0.21093618112012@news.panix.com> <50a9e5cf$0$21863$c3e8da3$76491128@news.astraweb.com> <roy-03667B.09591919112012@news.panix.com>
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Roy Smith wrote:=0D=0A> =0D=0A> OK, I've just read back over the whole thre=
ad=2E  I'm really struggling to=0D=0A> understand what point you're trying =
to make=2E  I started out by saying:=0D=0A> =0D=0A> > Use a list when you n=
eed an ordered collection which is mutable (i=2Ee=2E=0D=0A> > can be altere=
d after being created)=2E  Use a tuple when you need an=0D=0A> > immutable =
list (such as for a dictionary key)=2E=0D=0A> =0D=0A> To which you obviousl=
y objected=2E  So now you write:=0D=0A> =0D=0A> > I think a tuple is an imm=
utable sequence of items, and a list is a=0D=0A> > mutable sequence of item=
s=2E=0D=0A> =0D=0A> So how is that different from what I said?  Is this who=
le argument=0D=0A> boiling down to your use of "immutable sequence" vs=2E m=
y use of=0D=0A> "immutable list"?=0D=0A=0D=0A=0D=0A'''=0D=0ARoy:=0D=0A> Use=
 a list when you need an ordered collection which is mutable (i=2Ee=2E=0D=
=0A> can be altered after being created)=2E  Use a tuple when you need an=
=0D=0A> immutable list (such as for a dictionary key)=2E=0D=0ASteven:=0D=0A=
I keep hearing about this last one, but I wonder=2E=2E=2E who *actually* do=
es =0D=0Athis? I've created many, many lists over the years -- lists of nam=
es, =0D=0Alists of phone numbers, lists of directory search paths, all sort=
s of =0D=0Athings=2E I've never needed to use one as a dictionary key=2E=0D=
=0A'''=0D=0A=0D=0ATo me this is more of a question than an argument=2E Now =
moving=0D=0Aon to your specific example=2E=0D=0A=0D=0A'''=0D=0Adef extract_=
stack(lines):=0D=0A    "in traceback_helper module "=0D=0A    header =3D li=
nes[0]=0D=0A    stack =3D []=0D=0A    for line in lines:=0D=0A        m =3D=
 frame_pattern=2Ematch(line)=0D=0A        if not m:=0D=0A            contin=
ue=0D=0A        frame =3D (m=2Egroup('path'), m=2Egroup('function'))=0D=0A =
       stack=2Eappend(frame)=0D=0A    # [Convert to tuple and return after =
finished building stack=2E]=0D=0A    return (header, stack)=0D=0A[=2E=2E=2E=
]=0D=0Adef main(args):=0D=0A    crashes =3D {}=0D=0A    [=2E=2E=2E]=0D=0A  =
  for line in open(log_file):=0D=0A        if does_not_look_like_a_stack_du=
mp(line):=0D=0A             continue=0D=0A        lines =3D traceback_helpe=
r=2Eunfold(line)=0D=0A        header, stack =3D traceback_helper=2Eextract_=
stack(lines)=0D=0A        signature =3D tuple(stack)=0D=0A        if signat=
ure in crashes:=0D=0A            count, header =3D crashes[signature]=0D=0A=
            crashes[signature] =3D (count + 1, header)=0D=0A        else:=
=0D=0A=0D=0A            crashes[signature] =3D (1, header)=0D=0A'''=0D=0A=
=0D=0ASeems to me that Steven is suggesting that stack (after being built)=
=0D=0Ashould converted to a tuple before being returned, because a "stack" =
=0D=0Afor any unique exception should be unique and immutable=2E You do thi=
s=0D=0Aanyway; you just do it before putting it into a dictionary rather=0D=
=0Athan before returning it=2E=0D=0A=0D=0ASame net effect (as long as you d=
o not modify `stack` later), so no =0D=0Areal argument=2E=0D=0A=0D=0A=0D=0A=
~Ramit=0D=0A=0D=0A=0D=0AThis email is confidential and subject to important=
 disclaimers and=0D=0Aconditions including on offers for the purchase or sa=
le of=0D=0Asecurities, accuracy and completeness of information, viruses,=
=0D=0Aconfidentiality, legal privilege, and legal entity disclaimers,=0D=0A=
available at http://www=2Ejpmorgan=2Ecom/pages/disclosures/email=2E