[Visualpython-users] New Windows VPython

Bruce Sherwood bas at andrew.cmu.edu
Tue Dec 25 07:13:57 CET 2001

I'm not sure how to say it any more plainly than I've already said it, but 
I'll try once more.

NOTHING has changed in VPython that forces you to use the new division 

What has changed is that you MAY if you wish use the new division 
operators, even if you use Numeric arrays. The problem was that Numeric 
didn't recognize and process the new "true division" and "floor division" 
operators present in Python 2.2. There is no "fork" of Numeric. I've 
submitted the additions for inclusion in the next release of Numeric and 
been thanked for doing the work and told that many people were asking for 

But if you don't want to use the new division operators, DON'T put "from 
__future__ import division" in your programs! Including when you're using 

As to the student issue: There is no theorizing nor condescension in this. 
The actual data are that very smart college freshmen with very high SAT's 
etc., but who often have never written a computer program before, 
frequently make the "mistake" of writing such things as 1/2 thinking that 
this means the same as 0.5, because that's what it means in all other 
environments, including their pocket calculator. And they and their 
instructors find it difficult to track down why the program fails, because 
the difference between 1/2 and 1./2 is awfully subtle and hard to pick up 
in proofreading. I have a Ph.D. in physics,  done a lot of system software 
work including creating a respectable programming language (cT), and I make 
this "mistake" too when doing scientific programming. I repeat that this is 
about the only significant problem our students have had with Python. Can 
you present data that our students don't have a serious problem with this 
issue? Remember too that this is in the context of a physics class, not a 
computer science class, and we can't afford to spend time on teaching picky 
details of syntax.

Until now there was nothing we could do about this. We did not want to do 
what the Alice project did, which was hack Python to fix the problem, 
because this would be a "fork" and make our Python different from the world 
Python. Now with Python 2.2 we can teach our students to insert "from 
__future__ import division". And we can try to teach students that when a 
program fails, they should check to make sure that they've inserted this 

It is at least a reasonable question whether to drive Python or VPython 
with the "-Qnew" command-line option which has the same effect as the 
import statement. On balance, we think we shouldn't make this the default 
run mode in our local classroom VPython environment, because our students 
may well run Python and/or VPython in environments other than our classroom.

I will attempt to say nothing more about any of this.

Bruce Sherwood

--On Monday, December 24, 2001 21:14 -0500 Arthur Siegel 
<ajs at ix.netcom.com> wrote:

>> You've jumped the gun, but your input is useful nevertheless.
> I'm not sure how.  I am reading your message to say that the copy
> of Numeric that is downloaded with VPython has been patched.
> And since I am directing users of PyGeo to VPython, I am directing
> them to a forked version of Numeric. Which is somehow horrid to me.
> What am I missing.
> As to the rest -  I should probably keep my peace.
> I've pissed off enough people and caused myself enough
> grief in the course of it.
> But is all quite, quite incredible to me.
> I think the importance you attach to this issue is monumentally
> overstated, and overwhelmingly condescending.
> Now you are further saying that your students can't even be
> trusted to be able to handle the from __future__ statement
> all my their little bitty selves.
> Suffice it to say that am I sure the hell glad I'm not in
> school anymore.
> Art

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