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<H1>[pycrypto] Python 3.x vs. Python 2.1 - prep the axe</H1>
<B>don at amberfisharts.com</B>
<A HREF="mailto:pycrypto%40lists.dlitz.net?Subject=%5Bpycrypto%5D%20Python%203.x%20vs.%20Python%202.1%20-%20prep%20the%20axe&In-Reply-To=4D1972A2.4080305%40gmx.li"
TITLE="[pycrypto] Python 3.x vs. Python 2.1 - prep the axe">don at amberfisharts.com
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<I>Wed Dec 29 11:21:57 CST 2010</I>
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<PRE> Hi
If the only occurrence of this problem is with divisions by 2 then
couldn't you use a>>1 instead?
cheers and great to see some more effort and progress on py3k support.
//Lorenz
On Tue, 28 Dec 2010 00:16:18 -0500, Thorsten Behrens <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">sbehrens at gmx.li</A>>
wrote:
><i> On 12/23/2010 11:51 PM, Thorsten Behrens wrote:
</I>>><i> On 12/23/2010 9:18 PM, Dwayne C. Litzenberger wrote:
</I>>>><i> Also, down the road, I could be convinced to drop Python 2.1
</I>>>><i> support, if I
</I>>>><i> had some concrete examples showing that the result would be
</I>>>><i> substantially
</I>>>><i> less error-prone, easier to maintain, etc.
</I>>><i> So far, it doesn't look like that's needed. dict.has_key() cannot be
</I>>><i> replaced with "in" for 2.1, but 2to3 seems to handle it fine.
</I>><i>
</I>><i> I've run into a bit of a snag. The / operator in 2.x returns an int,
</I>><i> and
</I>><i> in 3.x it can return a float. This causes an infinite loop in
</I>><i> numbers.py. I can solve it with //, which is supported from 2.2 on,
</I>><i> but
</I>><i> not in 2.1.
</I>><i>
</I>><i> I've pasted the offending code snippet from numbers.py below, in the
</I>><i> form that doesn't cause an infinite loop in 3.x.
</I>><i>
</I>><i> I'm at a bit of a loss here. int(math.floor(a/b)) is not an option
</I>><i> due
</I>><i> to the size of the operands - it actually fails on 2.1, and gives
</I>><i> incorrect results on 3.x. That means I am stuck with //.
</I>><i>
</I>><i> I don't know how to "import something" and have "something" show up
</I>><i> in
</I>><i> the namespace above. I don't think it works that way, unlike a C
</I>><i> #include. That means I can't just bring the right function in
</I>><i> depending
</I>><i> on version. And even if I could, 2.1 doesn't have the "as" keyword,
</I>><i> so
</I>><i> it would never show up with the right numbers.getStrongPrime name
</I>><i> anyway, even _if_ such nested namespace manipulations were supported.
</I>><i> Which I don't think they are.
</I>><i>
</I>><i> I can't just "if sys.version" the offending code snippet, either: 2.1
</I>><i> will still complain that // is a syntax error.
</I>><i>
</I>><i> We could duplicate the code and have setup.py bring in a
</I>><i> special-cased
</I>><i> numbers.py for 2.1. I'm not sure how to do that with setup.py, but
</I>><i> there's got to be a way, even if it's just renaming files as needed.
</I>><i>
</I>><i> But that means duplicating an entire module, which is ugly. And I
</I>><i> can't
</I>><i> guarantee that this is the only occurrence of / that causes issues.
</I>><i> In
</I>><i> fact, I'd wager some beer that it likely isn't.
</I>><i>
</I>><i> If you can think of a reasonably clean way of handling the "/" vs.
</I>><i> "//"
</I>><i> issue - or if anyone else can - please share.
</I>><i>
</I>><i> Barring that, I think my message is: If Python 3.x is to be supported
</I>><i> without code duplication, Python 2.1 support may have to go.
</I>><i>
</I>><i> Yours
</I>><i>
</I>><i> Thorsten
</I>><i>
</I>><i> # if e is given make sure that e and X-1 are coprime
</I>><i> # this is not necessarily a strong prime criterion but
</I>><i> useful when
</I>><i> # creating them for RSA where the p-1 and q-1 should be
</I>><i> coprime to
</I>><i> # the public exponent e
</I>><i> if e and is_possible_prime:
</I>><i> if e & 1:
</I>><i> if GCD (e, X-1) != 1:
</I>><i> is_possible_prime = 0
</I>><i> else:
</I>><i> # Python 2.1 does not understand //, and 3.x returns
</I>><i> a
</I>><i> float on /
</I>><i> # Infinite loop, wheee!!!
</I>><i> if GCD (e, (X-1)//2) != 1:
</I>><i> is_possible_prime = 0
</I>><i> _______________________________________________
</I>><i> pycrypto mailing list
</I>><i> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
</I>
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