Is Python a functional programming language?

[travis+ml-python at subspacefield.org]

On Mon, May 10, 2010 at 08:45:51PM +0100, Nobody wrote:
> On Tue, 11 May 2010 00:24:22 +1200, Samuel Williams wrote:
> > Is Python a functional programming language?
> Not in any meaningful sense of the term.

LOL

> > I heard that lambdas were limited to a single expression,
> 
> Yes. In a functional language that wouldn't be a problem, as there's no
> limit to the complexity of an expression. Python's expressions are far
> more limited, which restricts what can be done with a lambda.

One very annoying thing in Python is the distinction between
statements and expressions.

Ever since learning LISP (well, Scheme) in S&ICP I find myself
frequently annoyed by this pointless distinction, started by
C (or earlier), and propogated without much thought.

Often I'll want to write a lamda that, say, prints something, or
modifies a global variable, and find that, well, it's either
impossible or beyond my interest in figuring it out.

It appears there is finally a ternary operator (for making if/else
into "expressions"):
http://en.wikipedia.org/wiki/Ternary_operation#Python
Maybe it will grow on me - it makes sense in English, but on
first glance I thought the programmer suffered from dyslexia.

To be fair, it appears that Python's whitespace-sensitive syntax sort
of precludes the "make a complex function on one line" that is typical
of languages which don't have statement/expression distinctions, but
I'm not convinced it couldn't be solved, perhaps by allowing anonymous
functions to span multiple lines, just like named functions.

> > Finally, even if Python supports functional features, is this a model that
> > is used often in client/application code?
> 
> Not really. List comprehensions are probably the most common example of
> functional idioms, but again they're limited by Python's rather limited
> concept of an expression.

Map/reduce, lambda, apply, that kind of stuff... kinda similar to
functional languages.

But "statements lack any side effects"?  No way.

In fact, a common distinction you'll see observed, but not always, is
that "statements may have side effects, expressions do not".

For some definitions of "functional language", there are no
side-effects, so there is no need for a statement which doesn't
evaluate to a value, so there is no need for a statement/expression
distinction, so everything is an expression.

You may have seen Paul Graham's other article about Python and LISP:
http://www.paulgraham.com/icad.html

Upon re-skimming it, I find myself wondering if I got the
expression/statement annoyance from his pages, or from my own
experience.  I can't remember :-) Probably it was an annoyance that I
hadn't put my finger on until he spelled it out for me, like a
splinter in my mind :-)

He obliquely references my other pet peeve, the global/class/local
distinction, completely ignoring arbitrarily-nested lexical scoping.
From what I've read in this thread, there's a recent "nonlocal"
declaration that sounds like it might accomplish something useful in
this regard.

(I still haven't figured out how he managed to use lexical closures in
 his web server to allow one web page to use another to allow the user
 to select and return a value, like a color from a color wheel, unless
 he implemented his own web server in LISP, since HTTP is stateless).

I really like Scheme's clean syntax (never learned Common LISP, sorry,
too much to remember) but frankly, I've never looked at a problem and
said, "you know, Scheme would be perfect for this".  Maybe if I was
writing a program that did optimizing transformations on abstract
syntax trees, or something.  And since Scheme has never come in handy,
I never bothered with Common LISP.  I feel similarly about ML, OCAML
and Haskell... maybe one day when I'm bored, not today, not this
project.

So in the end, I find myself using python more than anything else,
fully acknowledging its warts.  I used to admire its simplicity, but
now with decorators, iterators, generators, metaclasses, and the
proliferation of special method names, I have to wonder if that still
holds true...  certainly I understand 90+% of python programs, but
do I understand that proportion of the constructs?

PS: Why do people call LISP object-oriented?  Are they smoking crack?
    No classes, no methods, no member variables... WTF?
-- 
A Weapon of Mass Construction
My emails do not have attachments; it's a digital signature that your mail
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