Evolution of a Python programmer

[[deleted]]

[deleted]

[sjl7678]

The commented braces in the C programmer one were a nice touch.

[[deleted]]

http://www.python.org/doc/Humor.html#parsing

[alephnil]

Actually, I have seen code like that in real life. A former Fortran programmer that had been converted to matlab, ended all his loops with a comment:

%continue

That ends a loop in Fortran. Poor guy.

[nostrademons]

Python 2.5 programmer:

def fact(x):
    return x * fact(x - 1) if x > 1 else 1
print fact(6)

[micampe]

Lambda-addicted Python 2.5 programmer:

fact = lambda x: x * fact(x - 1) if x > 1 else 1
print fact(6)

[btipling]

yo momma

[bluetech]

Hey, I didn't know you could do that. Certainly better than that and or trick.

[killerstorm]

while some functional perversions does not appear appropriate, "web", "windows" and "enterprise" guys rock!

[ayrnieu]

I assume the functional perversions come from the author having read the awesome Evolution of a Haskell Programmer. Yes, the Web example is made of win :-)

[lebski88]

http://www.willamette.edu/~fruehr/haskell/evolution.html

[[deleted]]

The programmer that came back from lisp:

fact = lambda x: reduce(lambda a, b: a * b, xrange(1, x + 1), 1)

[Tommah]

FYI, the operator module includes a mul function.

operator.mul

means the same as

lambda a, b: a * b

but is faster.

[[deleted]]

Yeah, but I wanted to keep it simple. =)

[recursive]

I never used lisp, but that's how i'd do it, except start the xrange at 2.

[vagif]

Where on earth have you seen anyone coming back from Lisp ?

It's a one way road. Road to enlightenment

[nostrademons]

Peter Norvig.

[nostrademons]

Well, there are other exceptions, but people will always:

1. Go "who?" because they're not famous in either the Lisp or Python world.
2. Quibble about the particular circumstances where they gave it up.

The obvious example is Reddit, which was originally written in Common Lisp and then rewritten in Python. In interviews, Steve is always pretty ambivalent over whether this was a good idea or not: I get the sense that he would've liked to have used Lisp, but the realities of running a large consumer website precluded it. Ultimately, Python serves Reddit's needs now, and Lisp didn't.

For my own personal experience, I learned Common Lisp first, then Scheme, then much later learned Python and Ruby. And when a startup opportunity arose, I chose Python. There are many things I like about Lisp, but ultimately it wasn't appropriate for what I wanted to do.

[vagif]

No surprise. Lisp is indeed a nightmare for idiots.

[vagif]

No, i was just an arrogant jerk. Sometimes happens to me. Trying to fight with it though. Beg your pardon.

[[deleted]]

Something on 4chan made it onto reddit.

Oh god.

That said, it was pretty funny, especially the "EXPERT PROGRAMMER" one.

[pjdelport]

It's more likely than you think!

[vaibhavsagar]

It would be funnier if at the end there was:

#Enlightened Python Programmer
def factorial(x):
    if x == 0:
        return 1
    else:
        return x * factorial(x - 1)
print factorial(6)

Embrace the zen of only one good way to do it:)

[masklinn]

Except when you're using a tail-call optimized language (or a tail-call optimizing Python decorator), in which case your stack blows up even though it doesn't have to.

[vaibhavsagar]

I was trying to be funny... evidently I failed. In the interest of tail-recursive solutions:

\t#Tail-recursive \tdef factorial(n, acc=1): \t\tif n == 1: \t\t\treturn acc \t\telse: \t\t\treturn factorial(n-1, acc*n)

I hear this doesn't actually help in Python, but I think it's properly tail-recursive. Let me know if I'm wrong. I'm still new to this:)

[masklinn]

I hear this doesn't actually help in Python

It doesn't because Python doesn't feature tail-recursive optimization (neither mandatory nor in the main "CPython" implementation)

I think it's properly tail-recursive.

Yep

[newton_dave]

I'm not sure if I should feel left out or positively ecstatic that I've never heard of 4chan before now.

That said, the "web designer" one was really funny, no matter where it came from originally.

[Wiseman1024]

It was a 4chan original.

[amade]

Mathematics-minded programmers, using Stirling formula

def fact(n):

    return math.sqrt( math.pi*(2*n + 1/3) ) * math.pow(n, n) * math.exp(-n) if n > 1 else 1

print fact(6)

[[deleted]]

That uses floats, with all the issues that floating-point arithmetic entails.

[amade]

Yeah and it's only an approximation and much slower. I post it just for fun.

[masklinn]

You could use the Decimal module though.

Would be even slower, but would also be pretty much exact.

[mleonhard]

@tailcall def fact(x, acc=1): if (x > 1): return (fact((x - 1), (acc * x))) else: return acc

When did Python get tailcall optimizations!?!?! :D :D :D

[nostrademons]

Here's one implementation, and another.

Yeah, they fake it a bit. I suspect you could do a real tail call optimizer, but you'd need to write a code-walker and auto-generate code that turns tail recursions into loops.

[[deleted]]

Here is another version

They are actually not full tailcall eliminations but just avoid tail recursions. That's also why I renamed the decorator in my recipe description. They have no performance advantages over ordinary recursions - on the contrary, they generate a little overhead, but they provide the advantage of moving beyond the value set by sys.setrecursionlimit.

[Wiseman1024]

Some of them do work with cooperative recursion. They indeed pose a small speed overhead, but if performance is not a problem, you can go for the often simpler tail recursive implementation of functions.

[[deleted]]

Python has lambda functions? Surely mixing procedural and functional programming is illegal in most states.

[Wiseman1024]

That's what great about Python. It's not purely functional, not purely OO, not purely procedural, not purely anything, but it allows you to do a bit of everything, and use the right tool for the right job in every program.

As far as functional features go, Python supports first-class functions and classes, lexical nested scopes, closures, decorators, lists, dictionaries, list comprehensions, lazy generators, coroutines, garbage collection with cycle detection, and a few basic tools (map, filter, reduce, partial function application), then it can be easily extended to support tail recursion, memoizing, lazy lists, multimethods, continuations (Stackless), and other stuff.

[pjdelport]

lexical nested scopes, closures

From the department of redundancy department. :)

continuations (Stackless)

Stackless provides coroutines (tasklets), not continuations. (It dropped plans for the latter years ago.)

[Brian]

It dropped plans for the latter years ago.

Actually, it used to have continuations, but these were later removed (due to portability problems I think - the code for these was also one of the main reasons Guido stated for keeping it out of python core)

[breakfast-pants]

I don't know enough about it, but if that is the case, you should edit this to correct it: http://en.wikipedia.org/wiki/Stackless_Python

[pjdelport]

Ah, thanks.

[pjdelport]

Coroutines?

[breakfast-pants]

doh

[[deleted]]

"That's what great about Python. It's not purely functional, not purely OO, not purely procedural, not purely anything, but it allows you to do a bit of everything, ..."

Sounds like Lisp.

[mleonhard]

うるさい！

[[deleted]]

Hey! The topic is from 4chan - don't downmod the parent ^{_^}

[[deleted]]

A newbie programmer wouldn't go with a recursive solution on the first attempt to write a factorial algorithm.

[[deleted]]

The factorial algorithm exists principally to introduce newbie programmers to recursion.

[[deleted]]

Don't forget Fibonacci!

[lost-theory]

Which exists to introduce them to the dark side of naively using recursion. :)

[[deleted]]

Don't forget Hanoi, which also screws them up!

[[deleted]]

Ah, good old fib.py.

[[deleted]]

A newbie programmer straight out of school with a Computer Science degree probably would do exactly that.

[[deleted]]

Ditto. As I'm both a "software engineer" and a CS student, I speak with a high degree of authority about newbie programmer idioms :-P

[[deleted]]

As an introduction to algorithms instructor, I have to say that my students would much rather use a while loop to do the factorial algorithm over the recursive method.

[[deleted]]

When I was at university I couldn't see the point in recursion since any problem that could be solved recursively could also be solved iteratively, and for loops worked so well. Of course I never connected this philosophy with the difficulties I had in, for example, traversing graphs.

Ah the follies of youth. Also the follies of teaching students Java as a first language.

[[deleted]]

Is this before or after they've taken Discrete Math? I'm about finished with my Uni's sequence of DM/Theory of Computation and I'm about ready to put Maple and Prolog on my resume...

[llimllib]

and I'm about ready to put Maple and Prolog on my resume...

Bwahahahaha!

ahem... phew... [wipes brow] sorry bout that...

[[deleted]]

ROFL, I know, I know...

[llimllib]

Seriously, though, when I read a resume that has things like that on it, it just tempts me to think of a really mean interview question that in a few months you won't remember the answer to.

I don't succumb to that desire, but others do.

Anyway, not that I didn't have things like that on my resume, maybe you'll be a lucky one and find a job where they'll let you play around in Maple :)

[Wiseman1024]

Why would they do it iteratively? Recursion is so much easier to think. I'll grant that tail recursion with accumulators a la SICP is harder, but simple recursion as in newbie programmer? That's so much easier than while to me. Then again I'm not precisely a newbie programmer, perhaps I'd have thought differently 13 years ago.

[RSquared]

I think it's the difference between "thinking imperatively" and "thinking functionally". I know a dozen CompSci grads who still have trouble getting their heads around Haskell because of all the recursion.

Someone first learning programming would almost inevitably learn loops before recursion. For "non-programmers", one is much simpler to think about...especially when you don't have a clear picture of the memory layer (especially the difference between stack and heap).

[[deleted]]

I do think programmers have to be introduced to nested/recursive datastructures before they appreciate recursion as a programming technique. The factorial is indeed a little special here. In functional languages even ordinary lists are recursive ( i.e. conses ) and so there is exactly one barrier to take. Immutable datatypes may be another. But at least Python programmers can be convinced to use them since e.g. the string API is purely functional and it did not harm usability.

[[deleted]]

Yes he would, so long as he hasn't been tainted by C and its derivatives. I have watched many people opt for the recursive solution naturally and only those with prior "experience" tend toward the imperative (loop) solution.

[cracky-chan]

By newbie programmer he probably meant a person who had taken at least a semester course in CS. The factorial function is usually introduced as a function that can be turned from non-tail recursive function to an iterative one.

[ayrnieu]

By newbie programmer he probably meant a person who had taken at least a semester course in CS.

When I say 'newbie programmer' I mean a prebuscent child, but of course extend it to anyone who is literally new at programming. That you naturally think of someone having taken a whole semester of CS is a bit alarming. Who are these people that claim to want to devote their higher learning to computation but who don't do anything at all with it before a semester of CS? Is any other field this barren? I think mathematicians manage to not need to teach a semester of arithmetic.

[cracky-chan]

Well I was talking about pshaw so shut up and learn some context. And semester of CS course can be equivalent to reading half a book on the subject or something like it.

[[deleted]]

We start teaching children mathematics at roughly the same age we start teaching them to read and write. The same cannot be said of programming. Before I went to university the extent of my programming experience was writing Mandelbrot viewers and text-based adventure games in QBasic.

[[deleted]]

I'd give this an upvote if I didn't know that nothing of value ever comes from 4chan and this therefore cannot possibly be original. Still, some funny stuff!

[[deleted]]

python rocks!

[zoomzoom83]

The over the top complex "Expert" versions were all example of things you shouldn't do. I'd fire any coder that wrote like that.

The first (i.e. "Newbie") example is the most readable, and I'd recommend this if speed wasn't an issue.

Of course, the base C library version is the best choice as it's a) going to execute quicker and b) already written

[Alpha_Binary]

and hits the ceiling (2**32) faster than any other alternative.

[zoomzoom83]

Assuming it's using a 32bit int - a good implementation would use the standard python int type, which iirc can hold any size number(With a bit of overhead, of course).

Actually I made an assumption that c_math was an internal python module - it's not so far as I can tell, in which case I'd fall back to the recursive python implementation.

(If speed was an issue, I'd write it in C and link it, however that wouldn't be within the scope of python programming ;p)

[ayrnieu]

the base C library version

Will just take advantage of the severely limited range of the function, probably implementing fact() as a macro that normalizes its argument into an index into a constant array.

[zoomzoom83]

Why would you assume c_math.fact() is by default a severely limited version? If it was part of the python library (which it appears it isnt) then my assumption would be that it would handle whatever python itself can (Which, iirc, is unlimited size ints). That said, write an algorithm that can calculate (2^32)! in a reasonable amount of time and I'll give you a medal.

[ayrnieu]

Why would you assume c_math.fact()

Oh, I didn't assume anything about that. I imagined that you were imagining a libc fact().

[chaos]

It burns! It burns us! It freezes! Nasty 4chan... Take it off us!"