Raphael Sofaer rsofaer

Debugging and Exceptions

Agenda

Debugging Philosophy and Techniques
Basic Errors and Reading an Exception
Methods and the Stack, Reading a Backtrace
Error Classes, Raising and Rescuing
More Debugging Techniques, a Glimpse of Testing

Debugging in the Abstract

Living in the Command Line

Web programmers have to live on the command line. It gives us fast, reliable, and automatable control over computers. Web servers usually don't have graphical interfaces, so we need to interact with them through command line and programmatic interfaces. Once you become comfortable using the command line, staying on the keyboard will also help you keep an uninterrupted flow of work going without the disruption of shifting to the mouse.

Notes before we start

For any command we discuss here, the command man, short for manual, will give a (hopefully) detailed explanation of that command. Sometimes that explanation will be too detailed for you. When you get lost in a man page and you want to understand it, start again from the beginning of of the man page and keep repeating. Hopefully you will get further into the page each time you read it.

Metaphors

The command line is my home. I literally think of using the command line as walking around a building.

Wh

#WDI Installfest

We are going to install the tools necessarily to program with Ruby and Rails on your computer.

If you are on a Mac which is not running the latest version of OSX, please upgrade through the Mac App Store. Apple has made it easier to set up a computer for software development in OSX Mavericks, and keeping the differences between computers to a minimum will help us get everything installed quickly and correctly.

If you are unsure or run into problems during installation, stop and don't worry; We will finish up any of the loose ends on Installfest. Do not try to troubleshoot on your own, you might break your environment further.

	checking build system type... x86_64-pc-linux-gnu
	checking host system type... x86_64-pc-linux-gnu
	checking for python3.7... no
	checking for python3... python3
	checking for --enable-universalsdk... no
	checking for --with-universal-archs... no
	checking MACHDEP... checking for --without-gcc... no
	checking for --with-icc... no
	checking for gcc... gcc
	checking whether the C compiler works... yes

	describe("NiceTrie", function() {
	it("can be initialized", function() {
	var t = new Trie();
	});

	describe("with a trie", function(){
	var t;
	beforeEach(function() {
	t = new Trie();
	});

	<html>
	<head>
	<script>
	var flip = function(ele){
	ele.classList.toggle('flipped');
	}
	var move = 10;

	var moveBoss = function(){
	ele = document.querySelector('#boss');

	# Classes and Objects
	## Code Along

	require 'pry'

	story_hash = {
	"question" => "Welcome to the haunted hotel. What room would you like to go into?",
	"room 1" => "you're dead",
	"room 2" => { "question" => "You picked a good room. What would like to do?",
	"sleep" => "You're rested for the morning",

	class TreeNode
	attr_accessor :val, :left, :right
	def initialize(v)
	@val = v
	end

	def leaf?
	# A node is a leaf if it has no children.
	end
	end

	O(1) - Constant time
	"Get the first value of a list"
	"Random sample from a list"

	O(logN) - Divide and Pick
	Typical of algorithms that divide the input, then look at one of the sections
	Searching sorted data

	O(N) - For each ....
	Sum an array

	require 'benchmark'

	module RoflModule
	def rofladd(ping, pong)
	ping + pong
	end
	end

	RoflBlock = <<BLOCK
	def rofladd(ping, pong)