ASP.NET Web PDF Document Viewer/Editor Control Library

The boy/girl pairing example isn t particularly efficient because it checks every possible pairing. There are many ways of solving this problem in Python. The following was suggested by Alex Martelli: girls = ['alice', 'bernice', 'clarice'] boys = ['chris', 'arnold', 'bob'] letterGirls = {} for girl in girls: letterGirls.setdefault(girl[0], []).append(girl) print [b+'+'+g for b in boys for g in letterGirls[b[0]]] This program constructs a dictionary called letterGirl where each entry has a single letter as its key and a list of girls names as its value. (The setdefault dictionary method is described in the previous chapter.) After this dictionary has been constructed, the list comprehension loops over all the boys and looks up all the girls whose name begins with the same letter as the current boy. This way the list comprehension doesn t have to try out every possible combination of boy and girl and check whether the first letters match.

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In computer programming, a library is a collection of routines that can be called by separate programs, but that exist independently of those programs. For example, you could create a library to load and process a data file, and then use the routines in that library from any number of other programs. Earlier in this chapter, we looked at using the require command to load external files into your Ruby programs, and then we looked at how modules can be used to separate elements of functionality into separate namespaces. You can use both of these concepts, jointly, to make libraries in Ruby. At the start of this chapter you developed an extremely simple library called string_extensions.rb, like so:

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And you used this library with the following code:

require 'string_extensions' puts "This is a test".vowels.join('-')

Duplicate Layout. Right-click the duplicate layout that you just created, and select Rename Layout, naming the layout Explanation-Clipboard. Delete the Picture placeholder if you have one, and then add the clipboard graphic and three small boxes using the PowerPoint drawing tools. When you have nished, on the Slide Master tab, click Close Master View. In Slide Sorter view, hold down the Ctrl key as you select the Explanation slides that need a clipboard graphic, and then on the Home tab, in the Slides group, choose Layout. This will display an Of ce Theme window, as shown in Figure 8-36, that includes the Explanation-Clipboard layout you just created.

Nearly all libraries are more complex than this, but nonetheless, this is a basic demonstration of how a library works. Next we re going to look at the libraries that come with Ruby as standard, and look at a way to download and use libraries that other developers have made available on the Internet.

Nothing Happened!

Ruby comes with more than 100 standard libraries, as standard. They provide Ruby with a wide selection of functionality out of the box, from Web serving and networking tools through to encryption, benchmarking, and testing routines.

Clicking the Explanation-Clipboard layout option in this example applies all these changes to the selected slides, as shown in Figure 8-37, saving you the time and effort of adding the graphic to each slide yourself. For these particular clipboards, all you need to do next is add a check mark and a text box to each slide s graphic to match your sketches. You won t always have graphics that you can apply to multiple slides using custom layouts, but when you do, this technique helps you to make sure that your slides look good and also makes sure you don t accidentally alter the foundation graphics since they can only be changed in the custom layout.

Note Collectively the standard libraries are often called the Standard Library. When you see this term

(it s used particularly often in 16), it s important to remember it most likely refers to the collection rather than one library in particular.

Sometimes you need to do nothing. This may not be very often, but when it happens, it s good to know that you have the pass statement: >>> pass >>> Not much going on here. Now, why on earth would you want a statement that does nothing It can be useful as a placeholder while you are writing code. For example, you may have written an if statement and you want to try it, but you lack the code for one of your blocks. Consider the following:

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