>>> path = 'C:\nowhere' >>> path 'C:\nowhere' This looks correct, until you print it and discover the flaw: >>> print path C: owhere Not exactly what we were after, is it So what do we do We can escape the backslash itself: >>> print 'C:\\nowhere' C:\nowhere This is just fine But for long paths, you wind up with a lot of backslashes: path = 'C:\\Program Files\\fnord\\foo\\bar\\baz\\frozz\\bozz' Raw strings are useful in such cases They don t treat the backslash as a special character at all Every character you put into a raw string stays the way you wrote it: >>> print r'C:\nowhere' C:\nowhere >>> print r'C:\Program Files\fnord\foo\bar\baz\frozz\bozz' C:\Program Files\fnord\foo\bar\baz\frozz\bozz As you can see, raw strings are written with an r in front It would seem that you can put almost anything inside a raw string, and that is almost true.

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This is useful for stopping execution at a place where you want to see what s going on..

As you start your story template, you ve done your research with your audience and know that there is a shared sense of frustration with the delays on the project, but as an experienced project manager, you also know what the basic problems are and how they can be resolved. The Setting statement, shown in Figure 9-5, af rms We ve been racing to nish the project and earn our bonuses. The reference to the bonuses establishes right away something the audience personally cares about.

watch: Sets a condition breakpoint. Rather than choosing a certain line upon which to stop, you specify a condition that causes execution to stop. For example, if you want the program to stop when x is larger than 10, use watch x > 10. This is perfect for discovering the exact point where a bug occurs if it results in a certain condition becoming true. quit: Exits the debugger. A simple debugging session with your debugtest.rb code might look like this:

# ruby -r debug debugtest.rb Debug.rb Emacs support available. debugtest.rb:1:i = 1 (rdb:1) list [-4, 5] in debugtest.rb => 1 i = 1 2 j = 0 3 until i > 1000000 4 i *= 2 5 j += 1 (rdb:1) step debugtest.rb:2:j = 0 (rdb:1) i 1 (rdb:1) i = 100 100 (rdb:1) step debugtest.rb:3:until i > 1000000 (rdb:1) step debugtest.rb:4: i *= 2 (rdb:1) step debugtest.rb:5: j += 1 (rdb:1) i 200 (rdb:1) watch i > 10000 Set watchpoint 1:i > 10000 (rdb:1) cont Watchpoint 1, toplevel at debugtest.rb:5 debugtest.rb:5: j += 1 (rdb:1) i

Of course, quotes have to be escaped as usual, although that means that you get a backslash in your final string, too: >>> print r'Let\'s go!' Let\'s go! The one thing you can t have in a raw string is a final backslash In other words, the last character in a raw string cannot be a backslash Given the previous example, that ought to be obvious If the last character (before the final quote) is a backslash, Python won t know whether to end the string or not: >>> print r"This is illegal\" SyntaxError: invalid token Okay, so it s reasonable, but what if you want the last character in your raw string to be a backslash (Perhaps it s the end of a DOS path, for example.

In the storyboard sketches shown in Figure 9-6, the reference to racing in the Setting statement plays out as a motif on the Setting slide as a group of people running a race (upper left). Remember, introducing a motif to a BBP presentation is not a uffy nice-to-have addition in the story template and slides, but rather a strategy of introducing a familiar verbal and visual framework from the audience s long-term memory to introduce new information to their working memory.

This debugging session demonstrates stepping through the code, inspecting variables, changing variables in situ, and setting watch points. These are the tools you ll use 99 percent of the time while debugging, and with practice the debugging environment can become a powerful tool, much like irb. However, many Ruby developers don t use the debugger particularly often, as its style of debugging and its workflow can seem a little out of date compared to modern techniques such as test-driven development and unit testing, which we ll look at next. If the debugger seems like it could be useful, testing will make you drool.

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