Topic: if self.isCoder(): post() #Programming Thread (Read 886510 times)

Dutchling · « **Reply #3180 on:** October 22, 2012, 05:05:05 pm »

That gave me this:

Quote

TypeError: Can't convert 'bool' object to str implicitly

Which is kinda odd, as there is no boolean >.>

edit: the second one worked. Which I find odd. Why should it matter?
edit: Nevermind, I am an idiot. s.split() doesn't actually change the variable. I ALWAYS forget this...

GlyphGryph · « **Reply #3181 on:** October 22, 2012, 05:08:15 pm »

As Siquo said, pretty sure split just /returns/ the split string - it's not an in place operation.

Try:

Code: [Select]

s = 'aa>bb>cc'

print(s.split('>'))

Does that work for you?

Dutchling · « **Reply #3182 on:** October 22, 2012, 05:10:25 pm »

Yeah that worked. You ninja'ed my edit. I should probably write that down sometime, as I keep forgetting that a lot of stuff just return something instead of actually changing a variable.

GlyphGryph · « **Reply #3183 on:** October 22, 2012, 05:13:03 pm »

I'm pretty sure you don't even WANT it to be an in-place operation here, I'd imagine.

Remember that Python passes by reference, so you would have permanently changed 's' to an array.

dreadmullet · « **Reply #3184 on:** October 22, 2012, 07:25:49 pm »

Argh. In Code::Blocks, I have a static library project linked to an executable project. Whenever I change files in the static library project and recompile, the .o file for the executable project isn't updated. So nothing changes when I compile, I have to choose to rebuild everything. Annoying. Luckily, Code::Blocks allows me to specify a pre build command, so I just made it do "cmd /c del /q /s obj".

Nadaka · « **Reply #3185 on:** October 22, 2012, 10:03:50 pm »

Crash course on prototype based OOP in js.

Basic demonstration of prototype features.

Part 1:

Spoiler: the prototype (click to show/hide)

Code: [Select]

<html>
<head>
<title>JS prototype object oriented programming.</title>
<script type="text/javascript">
//This is js constructor. Yes it is just a method. Nothing special about it at all. 
function Foo() {}

//This is special. Foo has a prototype, just because this is js, and we do crazy shit up in here. We
//check to see if foo.bar() exists, and if it doesn't, we make it exist. This is boiler plate code. 
//All members and methods added to a prototype are public.
if (!Foo.prototype.bar) {
	Foo.prototype.bar = function() {
		alert("dude, I am this Foo's bar. The one that Foo's start with.")
	};
}

//This is how you create an instance of Foo, by using the new keyword. This is just like 98% of 
//other languages.
var aFoo = new Foo();

//
function a() {
	var aye = new Foo();
	aye.bar();
}

//The way this works is that for every object, it checks locally for a property, if it isn't found 
//locally, it checks the objects prototype. So if you "write" to an objects property, you add to its
//memory footprint. If I were making a lot of Foo's and changing their bar()'s it would eat up a 
//fair amount of memory because each one would have a seperate instance of the bar() method assuming
//no behind the scenes optimization. That memory usage could be reduced either by changing the 
//prototypes definition, or by defining the function elsewhere and mere adding a reference to it.
function b() {
	var bee = new Foo();
	bee.bar();
	bee.bar = function() {
		alert("I am this Foo's very own special bar that no one else has.");
	};
	bee.bar();
}

//this is where we change the definition of Foo dynamically. It affects all Foo's existing or about 
//to exist.
function c() {
	Foo.prototype.bar = function() {
		alert("I pitty the Foo!");
	}
}

//this just calls aFoo's bar().
function d() {
	aFoo.bar();
}

//this compares the prototype of aFoo to the current prototype of Foo for all browsers except ie <9
//note that the previous version of this actually compared undefined to undefined and always 
//returned true, my bad.
function e() {
	alert(Object.getPrototypeOf(aFoo) === Object.getPrototypeOf(new Foo()));
}

//This overwrites the prototype of Foo. Note that since any preexisting Foo's already have a 
//reference to the earlier prototype, they will still be using the old prototype and the old bar().
//Also, the e function will now alert false, because aFoo's prototype no longer matches 
//Foo.prototype.
function f() {
	Foo.prototype = {
		bar: function() {
			alert("foo you.");
		}
	}
}
</script>
</head>
<body>
<ol>
<li><button onclick="a(); return false;">This button creates a Foo and calls its bar()</button></li>
<li><button onclick="b(); return false;">this button creates a Foo, calls bar() changes the bar() of its instance and calls it again</button></li>
<li><button onclick="c(); return false;">this button changes the bar() of all Foo's</button></li>
<li><button onclick="d(); return false;">this button calls the bar() of a Foo that has existed before you clicked any of those other buttons</button></li>
<li><button onclick="e(); return false;">This is how you can check what prototype your object is using</button></li>
<li><button onclick="f(); return false;">This is me replacing the Foo'ing prototype</button></li>
</ol>
</body>
</html>

Mego · « **Reply #3186 on:** October 23, 2012, 01:18:00 am »

Quote from: Dutchling on October 22, 2012, 05:10:25 pm

Yeah that worked. You ninja'ed my edit. I should probably write that down sometime, as I keep forgetting that a lot of stuff just return something instead of actually changing a variable.

In Java and Python, there are no mutator methods for (String/str) objects. Every method that seems like it would change the contents of the object will instead return a new object without changing the original object.

Spoiler: Long Explanation (click to show/hide)

This is partly due to the fact that (String/str) objects can be expressed with literals, so mutator methods for literals would be very bad design. The only way you can change the contents of a (String/str) object is to use the assignment operator, which just makes the object point to a different memory location, without changing the actual data stored in memory.

Code: (Java) [Select]

// Let's suppose that String.replaceAll actually changed the contents of the string
String str = "A"; // The Java compiler will make "A" an interned String object, and str will refer to it.
str.replaceAll("A", "B");
String str2 = "A"; // We just tried to point to the interned String object "A" with another reference, except "A" is now "B". Therefore, every time "A" is encountered, it will be treated as "B". So, str2's contents will be "B".
System.out.println("A".equals("B")); // This will print true. That's bad. That's very bad.

In C++, the string class has mutator methods like string::insert and string::erase. Why is that not bad? Well, in C++, strings cannot be expressed as literals. When you have something like "abc", that is actually a character array, which is a primitive type and therefore can be instantiated with a literal. When a string object is instantiated with a literal, the string(char[] str) constructor is called. String objects don't directly reference literals, so therefore mutator methods are safe.

But wait... Character arrays are primitives in both C and C++, and the array access operator ([]) is a mutator! How can this work? Simple: C and C++ copy by value, rather than by reference. When you instantiate a character array with a literal, the array takes a copy of the contents of the literal, rather than becoming a reference to the literal. So, changing the contents of the array has no effect whatsoever on the literal.

GlyphGryph · « **Reply #3187 on:** October 23, 2012, 07:30:33 am »

Thanks, Nadaka! That was pretty thorough - I think I understand how it works now, which means I'll feel comfortable using it.

I'm not quite sure to the extent I /will/ use it, mind you.

Probably be limited to going back at the end and doing an efficiency run once the shape of everything is in place, since it's basically just shifting out the methods that only ever get defined once and for inheritance stuff which I might not need for my current project.

Thanks though, good explanation.

Nadaka · « **Reply #3188 on:** October 23, 2012, 07:45:41 am »

there is slightly more to it, there are ways to create private members/methods by declaring them inside the constructor, and a few other things but that was the basics for using the prototype itself though i didnt get around to multiple inheritance.

Dutchling · « **Reply #3189 on:** October 23, 2012, 05:35:21 pm »

Is there a way in Python to go through each key : value pair in a dictionary? I can't do it the way I do it with lists / strings because dict_var[x:y] gives an error. I know why it doesn't work that way, I just don't know any other way to do it.

Levi · « **Reply #3190 on:** October 23, 2012, 05:43:22 pm »

dict.items() turns it into a list of 2-element lists. Or you can get an iterator with dict.iteritems()

kaijyuu · « **Reply #3191 on:** October 23, 2012, 05:57:32 pm »

Code: [Select]

for x in dict.keys():
   #do whatever using dict[x] to reference each item in the dict individually

Dutchling · « **Reply #3192 on:** October 23, 2012, 06:33:17 pm »

Thank you both!

Nadaka · « **Reply #3193 on:** October 23, 2012, 08:29:43 pm »

Quote from: Nadaka on October 22, 2012, 10:03:50 pm

...

I updated that, made one mistake that needed fixing, and I added a bit more stuff.

MadocComadrin · « **Reply #3194 on:** October 23, 2012, 08:43:38 pm »

Quote from: kaijyuu on October 23, 2012, 05:57:32 pm

Code: [Select]
for x in dict.keys(): #do whatever using dict[x] to reference each item in the dict individually

IIRC, in newer versions of Python 3 and 2.X, you don't need to call keys().

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Author Topic: if self.isCoder(): post() #Programming Thread (Read 886510 times)

Dutchling

Re: if self.isCoder(): post() #Programming Thread

GlyphGryph

Re: if self.isCoder(): post() #Programming Thread

Dutchling

Re: if self.isCoder(): post() #Programming Thread

GlyphGryph

Re: if self.isCoder(): post() #Programming Thread

dreadmullet

Re: if self.isCoder(): post() #Programming Thread

Nadaka

Re: if self.isCoder(): post() #Programming Thread

Mego

Re: if self.isCoder(): post() #Programming Thread

GlyphGryph

Re: if self.isCoder(): post() #Programming Thread

Nadaka

Re: if self.isCoder(): post() #Programming Thread

Dutchling

Re: if self.isCoder(): post() #Programming Thread

Levi

Re: if self.isCoder(): post() #Programming Thread

kaijyuu

Re: if self.isCoder(): post() #Programming Thread

Dutchling

Re: if self.isCoder(): post() #Programming Thread

Nadaka

Re: if self.isCoder(): post() #Programming Thread

MadocComadrin

Re: if self.isCoder(): post() #Programming Thread