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Date: Mon, 2 Apr 2012 00:24:21 -0700 (PDT)
From: Yingjie Lan <lanyjie@yahoo.com>
Subject: Re: string interpolation for python
To: Adrian Hunt <cyborgv2@hotmail.com>
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Xref: csiph.com comp.lang.python:22441

Hi Adrian, see my comments below.=0A>________________________________=0A> F=
rom: Adrian Hunt <cyborgv2@hotmail.com>=0A...=0A>It could break old code...=
 okay you may say you should=E2=80=99nt allow =0A>certain characters but if=
 they're printable and used in a controlled=0A>environment those characters=
 can dramatically increase the security=0A>of a username and password.=0A=
=0A=0AWhat you said makes lots of sense to me.=C2=A0=0Aif strings are inter=
polated *automatically*.=0A=0ABut it won't and shouldn't.=0A=0AThey are cal=
led "Dynamic strings".=0ADynamic strings can achieve formatting,=C2=A0=0Abu=
t the mechanism under the hood differ=0Afrom common strings dramatically.=
=0A=0AMany here didn't realize that this is not=0Aanother formatting propos=
al, it is a new=0Akind of *expression*.=C2=A0=0A=0ATo have it in Python, we=
 will need=C2=A0=0Aa new kind of syntax to distinguish it=0Afrom other stri=
ngs, such as=C2=A0raw strings=C2=A0=0Aand the like. A raw string=C2=A0looks=
 like:=0A=0A>>> r'my\\ raw str'=0A'my\\\\ raw str'=0A=0AA dynamic string ma=
y look like this:=0A=0A>>> name =3D "Peter" #common string=0A>>> d"Thank yo=
u, $name$!" #dynamic string!=0A'Thank you, Peter!'=0A=0A=0AThe following ex=
ample would make it feel=C2=A0=0Aa lot more safe (suppose a =3D raw_input()=
):=0A=0A>>> a =3D=C2=A0'd"Are you $name$?"'=0A>>> print(a)=0A'd"Are you $na=
me$?"'=0A=0A>>> eval('d"Are you $name$?"')=0A=0A'Are you Peter?'=0A>>> d"It=
 contains $len(_.split())$ words!"=0A'It contains 3 words!'=0A=0AAn interes=
ting question might be:=0Awhat if a dynamic string is referring=0Ato anothe=
r dynamic string, which=0Ain turn refers back to the former?=0A=0AThe answe=
r is: no variable can hold=0Aa dynamic string itself, only its result,=0Awh=
ich can only be a common string.=0A=0AHowever, a infinite recursion may=C2=
=A0=0Aoccur if the eval function is used inside:=0A=0A>>> a =3D 'd"$eval(a)=
$"'=0A>>> eval(a)=0A=0AThis is just to show a dynamic string=0Ais really an=
 expression in disguise.=0ALike evaluating any expression containing=0Afunc=
tion calls, there is risk of getting into=0Ainfinite recursion.=0A=0ACheers=
,=C2=A0=0A=0AYingjie