McEs, A Hacker Life: On Python Coolness

Wednesday, November 28, 2007

On Python Coolness

wingo: Your hack only works if input sequence holds boolean (or integers for that matter) only. Note that Iverson’s Convention only says that the a boolean result is encoded as 0 or 1.

There is an elegant solution to your puzzle: use another lambda to work around and being syntactic:

all = lambda seq: reduce(lambda a, b: a and b, seq, True)

Moreover, unlike the Iverson page you linked to claims, at least with Python 2.5, Python does not use Iversion, but does the Perl-style convention of returning the first operand that determined the outcome of the expression, taking the short-circuit rules in mind:

>>> "m" and "n"
'n'
>>> [] and True
[]

Labels: Iverson, python, wingo

¶ 11:32 PM

Comments:

While the lambda you suggested does look somewhat more elegant than operator.and, it will run much more slowly. reduce will run far faster if it can call a C function like operator.and rather than a Python function like a lambda.

# posted by

Anonymous : November 29, 2007 4:11 AM

Language flamewars for fun: On ruby's coolness.

class Array
def all?
inject(true) { |all, n| all and n }
end
end

irb> [ true, true, true ].all?
=> true
irb> [ true, false, true ].all?
=> false

Stop this python madness ;)
info on inject (equivalent to reduce)

# posted by

arrêt sur image : November 29, 2007 4:45 AM

Heya Behdad!

As long as we are engaged in collective nit-picking: :-)

1. "Iverson", apparently. (I hadn't heard of it before reading that article.)

2. I believe that, according to Jones' article, that in Python == and >= follow iverson's convention. and and if are not functions, strictly speaking.

3. As you note, my definition of `all' is not the normal one, requiring numberic values. Yours is more general.

4. The point however was that python is such a smug language that doing evil is so attractive. It's like making fun of the teacher's pet. Amusing to be able to do numeric operations on the boolean type: True << (True + True) == 4. Nast!

5. Finally, my definition of all is non-optimal -- you can stop as soon as you have one falsy value. I don't know how to do that in Python as a one-liner, though.

Wingo

# posted by

Anonymous : November 29, 2007 5:17 AM

The comment tool sucks. Doesn't let me leave my comment. Trying a boring one with no HTML to see if it works.

# posted by

behdad : November 29, 2007 8:55 PM

Anonymous: operator.and doesn't work here. operator.__and__ is bitwise and, not logical and.

# posted by

behdad : November 29, 2007 8:55 PM

Wingo:

1. Yeah, muscle memory sucks.

2. I don't see the difference. between ==. vs and.

4. Yeah, I've got excited before about using int.__mul__ in reduce where * doesn't fit.

5. Can't think of either. The closest I got is: (a for a in seq if not a)

Cheers,

# posted by

behdad : November 29, 2007 8:56 PM

hello,

i came across your site while searching 'fribidi'. i am hoping you can help me.

i am trying to find a way to convert ISO-visual text to ISO-logical so that I can cut+paste into Word. currently, because the source is ISO-visual, i see the text reversed (instead of 'ABC', i see 'CBA').

i am not technically proficient, and i could not understand what I read on the fribidi website. perhaps you can help me?

thank you in advance!

# posted by

Anonymous : December 01, 2007 4:24 AM

FriBidi is mainly a tool for logical to visual conversion, but also works as an approximate visual to logical. Just run the command line tool fribidi and choose the right ISO charset. Feed it the input, get the output, like any standard Linux/Unix text tool.

# posted by

behdad : December 01, 2007 4:34 AM

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