[Tutor] Losing the expressivenessofC'sfor-statement?/RESENDwith example

[Alan Gauld]

"Stephen McInerney" <spmcinerney at hotmail.com> wrote

> I'm annoyed at how far offtopic and frankly rude the responses

Don;t get annoyed at off topic posts, that's all part of the fun in
a group like this which is aimed at teaching novices how to
program and specifically how to program in Python. The wider
issues are all part of the training.

As to rudeness, this is a very polite group by most internet 
standards,
but if anything I wrote upset you I apologise, it wasn't my intention.

> I'm just going to submit my doc change request to Fred Drake
> exactly as I was intending to before I sent the first mail.

That's fine and Fred may well incorporate it. Personally I believe 
that
would be a mistake as it sets a bad precedent. It may even encourage
C programmers to try to convert their C coding style into Python,
and that would be a big mistake - both for the individuals concerned
and for the Python community.

> I didn't get much decent opinion on my central question:

You got a lot of very good opinion, namely that you are comparing
apples and oranges. C's for loop is syntactic sugar for a while loop.
Python's for loop is a foreach construct for iterating over a 
collection.
Very different things, and impossible to compare sensibly.

> "isn't this idiom more restrictive than C/C++/Java (aka the
> rest of the universe),

But your central premis that C/C++/Java form the "rest of the 
universe"
is just plain wrong. There are many, many other languages in day to 
day use.
Infoweek and Computing magazines regularly run surveys of their 
readers
which show COBOL to be the most widely practiced language today (as
indeed it has been for the last 30 years!) - looking at job ads 
doesn't take
account of the fact that most COBOL jobs are with big corporations and
are often jobs for life! I know several of our (5000 or so) in-house 
COBOL
jockeys who have over 30 years service...)

> don't you agree it's badly explained in the doc (there is no basic
> advice to transform to while loop or else write generator), and the 
> doc
> should have a simple change

The docs explain how the python for loop works pretty well I think.
They do not explain the differences between Python's for loop and C's
for loop any more than they explain the differences between Pythons
lambda and Lisp's version. Whether the docs should do that is a
moot point that the maintainer (Fred) can decide.

> Show any of the code we discussed to non-Python programmers
> and they'll be lost.

That I doubt, most of it was generic apart from the generator 'yield'
construct. And anyone used to generators - Lisp, Ruby, Smalltalk
programmers would all guess at its function pretty well intuitively.

> follow-on question about generators returning a tuple
> (e.g. walking a pointer, and incrementing a count, let alone
> anything more complex)

Sorry, I missed it. Can you ask again in a separate thread and we
can take a look at it.

> - quibbling the motivation for the quicksort example I gave was
> clearly offtopic;

No, it was an example of how, by considering the actual purpose
of the code we can usually find a completely different solution to
any such problem. There are very few scenarios that actually require
that kind of low level algorithmic access in Python - algorithm
design being one valid example!

> the motivation was to give a legitimate example which clearly arises
> commonly.

And my point was that in Python it doesn't arise very commonly at all.
There is nearly always an alternative style of solution, often 
avoiding for
loops entirely.

> In any case, when we talk about people migrating from other 
> languages,
> C/C++/Java is ~60-95% of the audience, COBOL is irrelevant

Going by the posts we see on this list the majority of the folks 
coming
to python come from other scripting languages: PHP, Perl, Visual Basic
or from shell scripting (DOS Batch, VMS DCL  or Unix shell) or from
other high level languages like Rebol, Mathematica or Lisp. There are
also many first timers since python is fast becoming the teaching 
language
of choice in colleges and schools. We very rarely get questions from 
C/C++
programmers and only a few from Java. We have had at least one COBOL
programmer but I agree they aren't that common - mostly they are still
hacking away in COBOL! Where they might come from is using Python
as a replacement for their JCL scripts, and we have had a couple of 
those
at least...

> and PL/I is ancient history.

But we can learn from history and the lesson of PL/1 was - don't try 
to
create a language with all the features of every other language, it 
will
be a monster! I know you weren't trying to change the for loop merely
translate its style in the docs, but my point was that anyone looking
for all their best loved featires from language X in language Y is 
doomed
to failure.

> - This is offtopic, but the C for-loop syntax is very syntactically
> powerful, so when people perceive Python lacks it, they may baulk
> at that.

No arguments about its power, but anyone who gives up on a language
because one favourite control structure is missing is foolish in the
extreme.

> We have to do a better job selling why Python is better.

Its not better, just different. There are jobs that I would never try
to do in Python and for some I would pick C every time. For others
SQL or Prolog or even COBOL might be more appropriate.

> The C for-loop syntax itself is not error-prone at all.
> Unless you mean off-by-one errors etc., missing initializations, and 
> those
> are mostly semantic not syntax-related.

All I can say is that having seen several thousand C bugs pass
through my maintenance team I can tell you that for loop errors
are up there in the top 5 problem areas. Your list gives many but
there are also problems with side-effects introduced because of C's
assignment as an expression "feature". And if everyone rigorously
lint'ed their C then I agree many would be caught but I can attest 
that
many C programmers do not use lint - and indeed its not (readily)
available on some platforms (eg embedded controllers etc).

> >The C syntax is extremely odd to most programmers who haven't been
> >trained in it but in more traditional languages like Lisp, Cobol, 
> >Fortran,
> >Pascal, ADA, etc.
> Those were already dated in 1980

Well ADA didn't even exist in 1980. And new versions of COBOL and
Fortran have been standardised in the last 10 years. Admittedly
Borland Delphi is probably the last bastion of Pascal and Lisp
has had a long but loyal following since the early 60's with CLOS
standardised during the early 90's(?).

> - almost everyone these days learns C/C++/Java(/C#)

Those who go through University probably do, but many colleges
and high schools teach VB or interpreted languages (like python).
And scientists still get taught Fortran in many schools. And IS
programmers are still universally taught COBOL because it is still
the king of large scale data crunching.

> I am an EE who started out in the 80s with garbage like BASIC,
> Fortran, Pascal and assembly,

Me too, (except we didn't do Fortran) but I didn't find them garbage
(but I didn't like early BASICs its true), rather I found the 
different
approaches interesting. I also learnt Smalltalk at Uni - an advantage
for which I am immensly thankful since it opened my eyes to OOP
long before it became generally popular. I came to C during a vacation
job in 1985 and loved its conciseness and low level access, but I grew
to hate things like casting, and the arcane pointer syntax etc.

> we should at least make very basic accomodations for that
> migration reality. Specifically, give the people a hint to use
> while-loops and generators.

The docs describe while loops and generators. What we don't
want to encourage is C programmers coming to python and trying
to mentally translate their C code into Python by translating for
loops into while loops. That will nearly always be the wrong
approach. (K&R makes a similar point about discouraging Pascal
programmers from doing things like
#define BEGIN {
#define END }
in C.)

> >myList.sort()
>
> Alan - this was totally unnecessary and trashes the entire 
> (legitimate)
> context of my question.

Not so, it illustrates that the fundamental solution to your specific
example was in looking for a native solution to the problem - sorting
a collection. Using the built in functionality will nearly always be 
faster
and more efficient than building your own. And there are very few
cases where you need to build your own algorithms in python.

And as I said above we can't compare the general case because
C and python for loops are fundamentally different things.

I guess what I'm trying to say is that it is pointless trying to get 
the
documentation to provide pointers for any one language when there
are so many others out there(*). The purpose of the languages is
different, the syntax is different and so are the semantics of the
constructs.

(*) Interestingly my web tutor actually does take a comparative 
approach
teaching 3 languages in parallel. (One of which, JavaScript, uses the
C style for loop)  But this apparent contradiction in stance is in 
fact
because I believe that the syntactic differences in languages are
vastly overplayed. Learning programming happens at a much more
fundamental level than at the language syntax.

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld