[Edu-sig] Re: Python Programming: An Introduction to Computer Science

Kirby Urner urnerk at qwest.net
Fri Dec 12 14:00:29 EST 2003

I'm reading John Zelle's book, a real CS1 text book with exercises, using
Python as the language.

This is an exciting book (see my concluding remarks below).  I agree with
the blurbs on the back.  E.g. Russell May of Morehead State University
writes "This text does an excellent job of filling a gaping hole in the
Python community -- a textbook for an introductory computer science class...
It is as good a text as I have read for CS1."

Zelle has a lot of experience teaching CS1, back to Pascal days.  I trust
his sense of what belongs in a CS1 course in your average community or
4-year college.  It's a fairly gentle slope by design, and Python makes it

What frustrates me somewhat is that CS1 doesn't really show off the full
power of Python, and by the time we get to CS2 at Zelle's academy (and I'm
suspecting this will be somewhat typical), we're on to Java.  The reasoning
is solid:  real CS majors need exposure to a static-typed language, as well
as to more than one language.  I have no problem with this reasoning.

The frustrating part is this means cool CS2-level features of Python may not
get much if any airplay.  Syntax overloading is not taken up, and many OO
concepts get only initial treatment (e.g. no discussion of class vs.
instance properties/methods, nor of multiple inheritance).  No list
comprehensions, generators, regular expressions.  No passing of functions as
parameters to other functions.  No numarray, nor much use of the standard
library beyond math, random, string and Tkinter (which last is wrapped in a
simpler module, graphics.py).  No default or optional parameters. 

Try-except *is* covered, as is eval() and docstrings.

Again, I'm not questioning Zelle's judgment re what's appropriate to CS1.
He has long experience in this domain.  He's fully aware of what Python can
do, and just had to make these necessary cuts.  It's probably somewhat
painful to him as well, as when James Cameron (movie director) had to cut
out reel three of 'Aliens' in order to have it fit the movie-house time
constraints of the day (reel three is restored in the extended play

So let's assume a future in which Python is wildly successful as a CS1
language, but with this pattern of moving on for CS2, with the sense that
Python has well-prepared students to tackle something thornier.  Given this
bright future, I still have this lingering concern that Python may
eventually be typecast as a "beginner language" in the sense of being not
sophisticated enough for higher level development.

As Guido concludes in his short forward:  "Reader of this book,
congratulations!  You will be well rewarded for studying Python.  I promise
you'll have fun along the way, and I hope you won't forget your first
language once you have become a proficient software developer."

I think it's this hope that I'm echoing as a concern.  How will we ensure
that Python continues to receive attention even *beyond* its considerable
virtues as a beginner's language?

When I try to think about how to get deeper into Python within a CS
curriculum, I come up with a few ideas:

(a) push more compsci content into the earlier grades so that CS1 might move
more quickly from the beginning, and therefore get further.  E.g. if a lot
of the students coming in already know some Python, this would be ideal.

(b) keep the Python thread alive in CS2 even as Java is introduced, with the
potential to bridge the two using Jython.  This keeps Python around for
contrast.  This may actually be closer to Zelle's own approach, as he
mentions at his website using Python as "pseudo code" for Java-based
implementations (but then current Java doesn't do operator overriding, so
some cool features of Python would still be missed using this approach).

(c) think about returning to Python in CS3, if there is such.

(d) return to Python in some of the more specialized classes having to do
with graphics, computational geometry, statistics or other specific
applications (a recommendation similar to (c) I suppose).

(e) keep jiggering with the CS1 curriculum to squeeze more in, even if
students do not come in more prepared.

When considering option (e), my attention goes to the Point class.  If all a
Point does is hold x and y coords, then a class implementation seems like
overkill in Python.  You could get by with built-in tuples.  But what if we
make a Point slightly more interesting by making it a Vector?  Then you can
put in __add__ __sub__ __mul__ and __neg__, as well as length(self) and
maybe even dot(self,other) and cross(self,other) -- do one in the text,
leave the other for an exercise.  Then there's conversion to/from
polar/spherical coordinates.

Such a Vector might still be used as a parameter to Rectangle and Circle
constructors, as in the current version, i.e. it could start out as a simple
(x,y) container, and gradually mature as new OO ideas are mentioned.

Another approach would be to add a chapter called something like 'Looking
Ahead' or 'Advanced Python', wherein a lot of these cool features were
covered rather quickly and briefly, the intent being to give students a
foretaste.  Those students most enamored of programming and wanting to move
more quickly, could be directed to this chapter and a for-further-reading

However, none if this is about detracting from the worth of the text as it
stands.  I believe Zelle is perfectly positioned to press Python's case, and
is doing a very credible and creditable job of it.  

He's clear in his intro that his goal is less to teach Python than to give
an overview of important computer science concepts that students will
re-encounter in just about any language.  He's consciously eschewing certain
Python idioms (list comprehensions?) in favor of a more generic approach
because mastery of Python per se is not the main goal.  I understand his

Through his efforts, I'm hoping we quickly get to the point where "arguing
for Python" as a CS1 language becomes a no-brainer, i.e. it's not even a
point of controversy.  I think this text moves us a big step in that
direction.  It's clear, it works, and it should easily go into multiple
future editions.


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