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Explain xkcd: It's 'cause you're dumb.
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__NOTOC__{{DISPLAYTITLE:explain xkcd}}
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<big>''Welcome to the '''explain [[xkcd]]''' wiki!''</big>
<big>''Welcome to the '''explain [[xkcd]]''' wiki!''</big>

Revision as of 00:37, 4 March 2013

Welcome to the explain xkcd wiki!

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My optimizer uses content-aware inpainting to fill in all the wasted whitespace in the code, repeating the process until it compiles.
Title text: My optimizer uses content-aware inpainting to fill in all the wasted whitespace in the code, repeating the process until it compiles.


Adobe Photoshop is a commonly used software for image manipulation. One of its features is "content-aware inpainting", which allows the user to delete parts of the image and seamlessly replace the deleted sections with "patches" of texture from other parts of the image.

The GNU patch is a software program that replaces only parts of the code with an updated version, without requiring the user to download the entire source code. Here, it appears the author was told to "patch" the code, but used Photoshop to do this instead of GNU patch, with devastating results. Although the title text suggest that if you did this enough times the code would eventually compile, this would never happen. In fact, Photoshop could only edit an image of the text and not the text itself.

The comic blurs the difference between text (in which letters and symbols represent discrete values, such as 65 being the number for the letter A in the ASCII encoding standard, and it's relatively easy for a program compiler to interpret combinations of these values as keywords and other programming constructs) and graphics (where the letters and symbols in the comic are actually represented by pattern of colored dots). There are common and straight forward processes for converting text information to images, such as Printing, which can convert text to a graphics format very faithfully. The reverse, however, requires the use of OCR (Optical Character Recognition), which attempts to figure out which letter or symbol certain patterns of dots "look like". OCR could be effective in converting some of the image in the comic back to usable text, however it would fail on some of those patterns that have been mangled and don't look like any existing characters or symbols. The compiler can only operate on text data, so converting the graphic back into text would be a requirement to even begin to attempt to compile it, a step omitted in the title text.

The code appears to be written in Python, a programming language often referred to in xkcd. A few of the function names that can be recognized are "isPrime" and "quicksort", both elementary programming algorithms.

The title text also explains that patch used the content-aware inpainting to fill in all the wasted whitespace in the code. In Python, whitespaces are used as a part of the programming syntax (for example, new lines of code are used instead of semicolons (;), and indents are used instead of curly brackets.

The original code was likely as follows:

import re
def isPrime(n):
	if n<=1:
		return False
	for i in range(2, int(n**0.5)+1):
		if n%i==0:
			return False
	return True
def isPrimeRegex(n):
	if re.match('^1?$|^(11+?)\1+$', '1'*n): 
		return False
	return True
def quicksort(a):
	if len(a) < 2:
		return a
	l=[i for i in a if i<pivot]
	r=[i for i in a if i>pivot]
	return quicksort(l)+mid+quicksort(r)

isPrime and quicksort are standard python implementations of simple algorithms (although you would not generally write a sorting algorithm in python as there are built-in algorithms available). isPrimeRegex uses the re module to detect if a number is prime by seeing if a string containing that many 1s can be matched to 2 or more copies of some string containing at least 2 1s.


[The panel displays part of a code, in four different colors (red, light blue, green and purple) as well as normal black text, which due to image editing is difficult to read. The first and last line are partly obscured by the frame of the panel. Here below is an attempt to transcribe the code, using the sign "¤" for anything not easily transcribed. Feel free to add other signs instead of these that looks more like the one in the image (and also improve the attempted transcription if possible).]
impo¤l me
		retern F(ise
	for i irararre(2, nint *n**n+5)+5):
		if n i==0
	re¤ irn True
defesisPrimcieg ¤x(cx
	if ge¤inatcx(r'^(1?| ?.1+?)\+)$'*n )1'*n):
		rerjrn Fa( e
dql qlsorsorn(a :
	if ¤n(a < 2:
		eteturn a
	pi= =r fa[0]
	l=pi=for j ln a i< i<pi<(t]()
	r=[l=for f in a) r i>viviv](vo)
	r¤lrurrriklcksckt(l) + r ¤ ¤quickrort(r)
[Caption below the panel:]
Protip: If you don't have access to the GNU patch tool, you can use the Photoshop one.

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