The Python IAQ: Infrequently Answered Questions

http://norvig.com/python-iaq.html

by albertcardona • 16 years ago

83 36 16 years ago

norvig.com

ximeng• 16 years ago

Python infrequently asked questions, google cache at

http://webcache.googleusercontent.com/search?q=cache:norvig....

Seems a bit out-of-date (upcoming Python 2.5?), not sure why it's here really.

pilom• 16 years ago

Great article, bad title. Someone with more kharma mind changing it to Python Infrequently answered Questions?

TomasSedovic• 16 years ago

I agree.

The article actually contains the "if u cn rd ths..." phrase and it's a nice touch. However, it would be better to keep the original title and mention the phrase in the comments.

shabda2• 16 years ago

I don't get it anyway, if I can read this, why can I get a job in functional programming?

nene• 16 years ago

I think it is just taken out of the context from the article, where it's just below a code sample with a fair amount of lambdas in it.

trotsky• 16 years ago

even worse for me, I clicked to find out why employers like citi and BofA in the financial sector were no longer able to afford vowels for their programmers.

JustinSeriously• 16 years ago

It was a weird title. I did an an quick poll of two non-programmer, LOL-speak experts, and I got these answers:

- If you can read this, you can get a job in financial program (if there were any)

- If you can read this, you can get a job in functional programs/programming (if there were any)

I don't know what this proves.

albertcardona• 16 years ago

Regarding the "if thr wr any", and the rise of Haskell and Clojure, I wonder whether such caveat applies any longer.

As for content of the Python IAQ, I've enjoyed learning about two python idioms I had never known possible:

1. The ternary conditional operator:

x = <result> if <test> else <alternative>

2. Using or to assign an alternative value when the first is False or None

x = <option> or <option>

TallGuyShort• 16 years ago

Incidentally, most C-style-syntax languages have a ternary conditional operator, and I use it quite a lot for things like building strings, very small conditionals, etc.... When used correctly, it can improve readability and expressiveness quite a bit.

x = <test> ? <result> : <alternative>

Some times for slightly more complex expressions, I'll put them on separate lines so as to have a very compact if/else structure.

IgorPartola• 16 years ago

As pointed out in the OP, there are actually quite a lot of ways to simulate the ternary operator in Python. An interesting one is (result, alternative)[test]. If result and alternative are functions you could write it as (result, alternative)[test]().

And for desert: I love this syntax:

  if 0 < x <= 100: pass

For more info see: http://stackoverflow.com/questions/394809/python-ternary-ope...

adambyrtek• 16 years ago

It's worth noting that Peter himself mentions that most of the ternary tricks he describes are not very readable and wouldn't be considered Pythonic.

   Beautiful is better than ugly.
   Explicit is better than implicit.
   Simple is better than complex.

Personally I'd hate to see something like that in any real-world project.

   (test and [result] or [alternative])[0]

cema• 16 years ago

Depending on the language, it could be an idiom.

reinhardt• 16 years ago

"..and the rise of Haskell and Clojure.."

Is there any real world evidence of said claim, outside geek-fetish bubbles like HN ?

danio2• 16 years ago

Is there much benefit to

    fact = lambda n: _if (n <= 1) (1) (lambda: n * fact(n-1))

over

    def fact(n):
        if (n <= 1):
            return 1
        else:
            return n * fact(n-1)

1 line vs 5 lines doesn't seem like an advantage to me when it takes pretty much the same amount of time to read and understand the complicated 1 liner.

Is there more optimisation possible?

Kilimanjaro3• 16 years ago

Sometimes I put short ifs in one line, just personal taste

    def fact(n):
        if n<=1: return 1
        else:    return n * fact(n-1)

Kilimanjaro3• 16 years ago

Which I guess can be written like

   def fact(n):
        return 1 if n<=1 else n*fact(n-1)

kolektiv• 16 years ago

One of those times when I hugely miss languages with pattern matching/guards.

  fact(1) = 1
  fact(n) = n * fact(n-1)

Seems much more readable to me.

Goladus2• 16 years ago

     python -c "import _if; fact = lambda n: _if (n <= 1) (1) (lambda: n * fact(n-1)) ; fact(5)"

The main advantage of a 1-liner is that you can compose the whole thing and execute it without having to format anything. That is a nice feature for code that is only ever intended to be used once, such as from the python repl or some other shell. --Or more than once, for the duration of a session. It's a lot easier to use command history to get and modify a 1-liner than to replay a 5-line function definition.

When the code is primarily expressions, it's relatively easy to to this. Trying to do one-liners with regular python syntax can get tricky.

Also, if you have a series of similar relationships to present, it's often easier to line them up next to each other. You might cut 12 lines to 6 lines and the whole thing will be far clearer. Although in those cases, it's probably more effective to use a dictionary to achieve the same thing, with the advantage of data/logic separation.

jules2• 16 years ago

    fact = lambda n: 1 if n <= 1 else n*fact(n-1)

or, for that matter:

    def fact(n): return 1 if n <= 1 else n*fact(n-1)

gaius3• 16 years ago

They are of broadly equivalent complexity (if you are used to Python) and you can fit more of the former in an editor window.

I don't like tho' that "lambda" is a keyword in Python, I much prefer Haskell's \ or OCaml's fun.

d0mine• 16 years ago

   from math import factorial

   fact = lambda n: reduce(operator.mul, xrange(1, n+1), 1)

KirinDave3• 16 years ago

I dunno why people think functional programming jobs are vanishingly scarce. They are not. If you can demonstrate skill in functional languages, you might even get recruited.

It's true there are more wage-slave code-a-day jobs, but those jobs can be easily filled by uninspired hacks who are in it for the money. If you're reading this, the odds of you being one of those hacks is very low. The job market is smaller, but the workforce of talented functional programmers is much smaller, so the demand is still high.

And Clojure & Scala are even easier because you can get a java job and them worm them in. It's not difficult to make a compelling argument that Clojure & Scala are better at Java than Java is.

gaius3• 16 years ago

Functional programming jobs are scarce, but that's because no-one is a "functional programmer" in the same way that you might be a "PHP programmer". Instead you get lots of jobs where you happen to write a lot of code in a functional programming language but you don't look like a programmer in an organizational sense - you're an "analyst" or an "engineer" or whatever. That's where F# is making inroads.

strlen• 16 years ago

You're not going to do functional (or any other interesting) programming as an IT programmer in a generic financial services company.

If you work for an actual software company (or perhaps an innovative financial services company) as a software engineer (or even on an operations team in some cases e.g., Sysadmins at Google using Haskell, ops tools at Yahoo once built in OCaml), there's plenty of chances to do functional programming (or something else that interests you).

It's just generally people are programmed to think "it's just a job" and choose their jobs based on salary, name recognition, commute hours etc... (Some also have very specialized skills like systems programming or machine learning and aren't particularly interested in programming languages, although I think they're missing out)

KirinDave3• 16 years ago

I really don't understand your point. What is the difference between a "programmer" and an "engineer"? Why doesn't "functional programmer" as a category include things like "F#", which you suggest is a valid category.

As for me, I interviewed at several jobs that featured functional programming during my last jobsearch. I actually turned down offers that were not devoted to functional (or at least hybrid object/functional) technologies.

noahlt• 16 years ago

It's also worth noting that, in Python 2.6 and higher, we DO have a ternary operator:

    x = 3 if foo() else 6

tomotomo• 16 years ago

If u cn rd ths... then you may speak Hebrew or Arabic, which are basically written without vowels.

anateus• 16 years ago

Some of the responses are outdated, here's one of the things that is now part of python:

Python 2.5 introduced defaultdict in the collections module:

   from collections import defaultdict
   d = defaultdict(int)
   d['foo'] +=1 # look ma! no error!

For this application, if you're using Python 2.7 there's now a Counter in collections, you can do the same as above, just call Counter(). You can also do:

   c = Counter(iter) # iter is an iterable. It will count the elements!

The Python IAQ: Infrequently Answered Questions

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