Programming, computers, etc. [Serious]

[Dreams]

Now that's just contradictory

[Anonymously Famous]

I think it will get more people to try Linux out (though live CDs are pretty cool, too).

[atomtengeralattjaro]

I've been spending the good part of today on learning linux bash scripting, I'm writing a test tomorrow..

[Dreams]

Good. Don't destroy system files.

[Anonymously Famous]

Bash scripting can be really powerful.

[atomtengeralattjaro]

My flash sig seems to not work properly all of a sudden.. it stops between the last and the first image, i think. I'm just gonna change it to a simple image, i guess, I don't bother with bugs that come out of nowhere..

[Anonymously Famous]

Maybe an update to Flash?

[atomtengeralattjaro]

i'm writing a tough Assembly test tomorrow, wish me kind registers!

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mov bed,atomtengeralattjaro

[Anonymously Famous]

May your registers behave themselves.

[atomtengeralattjaro]

and so they did Fortunately we had enough time, and I think I passed. Only for some reason when the program drew a triangle, it also drew a bunch of other lines in other places.. :S i guess i lost my way in the video memory somehow.

[Anonymously Famous]

It's easy to get lost in assembly.

[Anonymously Famous]

I feel bad double posting, but I found out something interesting today.

First, the known facts:
In Python, everything has a "truthiness" to it. That is, logically, everything is either True or False. If it's None, False, 0, 0.0, or the length of it is 0, it's considered to be False. Everything else is True (including functions and classes).

What I found out:
The logical "and" and "or" in Python don't always return True or False. They return one of the operands. "and" returns the first operand if it's "False-like" and the second one otherwise. "or" returns the first operand if it's "True-like" and the second one otherwise. Sure, you can "cast" it as a bool, but if you don't, it can lead to some interesting side effects.

Examples:

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5 and "Bob"

is "Bob"

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5 or "Bob"

is 5

[atomtengeralattjaro]

this truthiness thingy is spooky. Do you know any scenarios where this can be used? i think it would just confuse me, but it does seem interesting.

[Anonymously Famous]

Well, I don't know exactly when it would be used... It behaves exactly the way that you would expect it to in if statements and while loops. The truthiness thing exists in C/++, too. You can do "while(5){doStuffThatHopefullyEventuallyBreaksOutOfTheLoop();}". It only gets weird if you use it as a statement itself.

One possible use: Say you have 2 lists of Strings. The lists have the same length, just to make things simple. If an item in list1 is an empty string, you want to use the corresponding item from list2. There are several ways to do this. This is an unconventional one using "or":

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[i[0] or i[1] for i in zip(list1, list2)]

Here's one more like what you would expect:

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result = []
for i in range(len(list1)):
    if list1[i] != "":
        result.append(list1[i])
    else:
        result.append(list2[i])

Or, the same thing, as a list comprehension:

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[list1[i] if list1[i] != "" else list2[i] for i in range(len(list1))]

Still, it's just an oddity. If you want to force a boolean, you can use bool(a or b). It is a documented oddity. I just hadn't realized that it was there. Like I said, in most cases, it behaves as you would expect it to.

It also makes the implementation pretty easy, actually. For example:

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def customAnd(a,b):
    return a if not a else b

def customOr(a,b):
    return a if a else b

Voila! It all depends on the truthiness of a. In the implementation of the language, b isn't even evaluated unless it needs to be. I guess you could also use that side effect. For example:

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def printMe():
    print("Hello")
    return 0

def dontPrintMe():
    print("I should not print")
    return 1

printMe() and dontPrintMe() # This should only print "Hello"

[atomtengeralattjaro]

woah..
i'm lost.
i have no idea about the whole syntax in your first example, and i don't even know what "zip" does
And the last one is just plain weird. But it makes sense. Took me a while to get it though..

[Anonymously Famous]

zip takes n lists and produces one list. That list contains tuples (which could be considered a special type of list) of n elements - one from each list. It's defined to stop at the end of the shortest list. so zip([1,2,3], [4,5,6]) would produce [(1,4), (2,5), (3,6)]. So in that look for strings example, it goes through each element in the zipped list, and does firstValue or secondValue. If firstValue seems False (i.e. It's the empty string), it uses the second value.

A modified first example (the C/++ code):

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if(5)
{
    cout<<"5 is considered to be \"True\" in C++";
}

In Python, "x if condition else y" is kind of their ternary (?) operator. If the condition is true, it results in x. If not, it results in y.

[atomtengeralattjaro]

I see! I think it's clear now.

[Anonymously Famous]

Speaking of Python...

I just learned of a site called Udacity today. It's kind of like an online school, with free online courses. It's not accredited, so you don't get a degree, but the instructors are university professors or professionals in their field. They're mostly programming classes, and the language used, as far as I can see, is Python 2.7 (though the theory learned is valuable regardless of the language). I may or may not have signed up today and enrolled in all of the classes. Simultaneously... Good thing there's no strict deadline!

[atomtengeralattjaro]

woah and it's free! as in free beer?

[Anonymously Famous]

It's free as in free online classes.