Python Programming

Exercises Ikh Python Scientific Programming

Wed, 22 Feb 2012 23:16:56 GMT

Make a program that simulates flipping a coin N times. Print out tail or head for each flip and let the program count the number of heads. Hint Use r random.random and define head as r lt 0.5 or draw an integer among 1, 2 with r random.randint 1,2 and define head when r is 1. Name of program file flip_coin.py. o Exercise 8.2. Compute a probability. What is the probability of getting a number between 0.5 and 0.6 when drawing uniformly distributed random numbers from the interval 0,1 To answer...

Representing documents with XML 1 IronPythonIntroduction

Wed, 22 Feb 2012 22:17:49 GMT

XML is a text-based format that uses tags to structure data. XML is certainly no silver bullet when it comes to persisting data it's generally verbose and, for complex data structures, inefficient. On the other hand, XML is a text-based format. If something goes wrong with your program, it's easier to see what's going wrong than with a binary format. An XML document will look something like the following segment lt xml version 1.0 encoding utf- 8 gt lt rootelement gt lt childelement1 attribute...

callable global function PythonTutorial

Wed, 22 Feb 2012 15:20:19 GMT

In Python 2, you could check whether an object was callable like a function with the global callable function. In Python 3, this global function has been eliminated. To check whether an object is callable, check for the existence of the_call_ special method. In Python 2, the global zip function took any number of sequences and returned a list of tuples. The first tuple contained the first item from each sequence the second tuple contained the second item from each sequence and so on. In Python...

Other kinds of tests PythonProgramming

Wed, 22 Feb 2012 08:23:28 GMT

Lucky for us, the other comparison operators are easier to remember less than lt , greater than gt , and not equal to . You can also use lt gt for not equal to, but most people use . You can also combine gt or lt with to make greater than or equal to gt and less than or equal to lt . You might have seen some of these in math class. You can also chain two greater-than and less-than operators together to make an in-between test, like this This will check if the variable age has a value between,...

Brief Introduction to SNMP Python for Linux System

Tue, 21 Feb 2012 18:35:11 GMT

The 10,000 foot view of SNMP is that it is a protocol for managing devices on an IP network. Typically, this is done via UDP ports 161 and 162, although it is possible, but rare, to use TCP as well. Just about any modern device in a data center supports SNMP this means it is possible to manage not only switches and routers, but servers, printers, UPSs, storage, and more. The basic use for SNMP is to send UDP packets to hosts and to wait for a response. This is how monitoring of devices occurs...

Conditionals and loops IronPythonIntroduction

Tue, 21 Feb 2012 03:05:06 GMT

Very often through the course of a program you'll need it to take different actions depending on some condition maybe finding the terminating condition of an algorithm, or responding to user input. The conditional statement in Python uses the if keyword. Every statement that starts a new block of code must be terminated with a colon. Indented code following the if statement will only be executed if the condition evaluates to True. As soon as your code is dedented, execution continues normally....

Private and public variables and methods Python Tkinter Programming

Sat, 18 Feb 2012 01:24:13 GMT

Unless you take special action, all variables and methods are public and virtual. If you make use of name mangling, however, you can emulate private variables and methods. You mangle the name this way Any name which begins with a double-underscore _ is private and is not exported to a containing environment. Any name which begins with a single underscore _ indicates private by convention, which is similar to protected in C or Java. In fact, Python usually is more intuitive than C or other...

Test Your Knowledge Quiz Vib Python Object Oriented Programming

Fri, 17 Feb 2012 11:35:20 GMT

1. What three things are required in a C-like language but omitted in Python 2. How is a statement normally terminated in Python 3. How are the statements in a nested block of code normally associated in Python 4. How can you make a single statement span multiple lines 5. How can you code a compound statement on a single line 6. Is there any valid reason to type a semicolon at the end of a statement in Python 7. What is a try statement for 8. What is the most common coding mistake among Python...

Coroutines Python Programming Techniques

Thu, 16 Feb 2012 22:51:20 GMT

Coroutines are functions whose processing can be suspended and resumed at specific points. So, typically, a coroutine will execute up to a certain statement, then suspend execution while waiting for some data. At this point other parts of the program can continue to execute usually other coroutines that aren't suspended . Once the data is received the coroutine resumes from the point it was suspended, performs processing presumably based on the data it got , and possibly sending its results to...

In many places it wont matter whether you pass in a sequence or an iterator In that case a function or method may just specify that it needs an iterable IronPythonIntroduction

Thu, 16 Feb 2012 22:01:35 GMT

Assigning to members of a list uses the same syntax. gt gt gt a 1, 2, 3, 4 gt gt gt a 0 ' a' gt gt gt a 'a', 2, 3, 4 gt gt gt a -1 'b' Deleting members uses the del keyword. Because you can modify a list by changing members or adding and removing members, it is a mutable datatype. The list has a close cousin that's immutable the tuple. TUPLES The tuple is a container object similar to a list. Tuples can be indexed in the same way as lists but, because they're immutable, you can't assign to...

Running Your Tests Follow Your Nose PythonTesting

Thu, 16 Feb 2012 04:07:28 GMT

So far, we've talked a lot about how to write tests, but we haven't said much about how to run them. We've had to explicitly tell Python which tests to run, and we've had the either worry about which version of Python we were using in the case of doctest or put an if _name_ '_main_' inside every module for unittest . Clearly, there's room for improvement, when it comes to running tests. Learn about a Python tool called Nose, which automatically finds and executes tests Learn how to make Nose...

Listing A function to compile and save or return assemblies from source code IronPythonIntroduction

Tue, 14 Feb 2012 04:46:06 GMT

from System.Environment import CurrentDirectory from System.IO import Path, Directory from Microsoft.CSharp import CSharpCodeProvider from Microsoft.VisualBasic import VBCodeProvider def Generate code, name, references None, outputDir None, inMemory False, csharp True params Compiler.CompilerParameters Configure the path c t . _ to save assembly outputDir Directory.GetCurrentDirectory asmPath Path.Combine outputDir, name '.dll' params.OutputAssembly asmPath params.GeneratelnMemory False else...

contents Python Tkinter Programming

Mon, 13 Feb 2012 15:36:50 GMT

preface xv special thanks xvii about the reader xix about the author xx conventions xxi about the cover xxii author online xxiii 1.1 Introduction to Python programming and a feature review 3 Why Python 4, Where can Python be used 5 1.2 Key data types lists, tuples and dictionaries 5 Lists 5, Tuples 7, Dictionaries 8 How do classes describe objects 9, Defining classes 9, Neat Python trick 10 9, Initializing an instance 10, Methods 10, Private and public variables and methods 11, Inheritance 11,...

wxPython PythonIntroduction

Mon, 13 Feb 2012 01:37:50 GMT

wxPython is a GUI toolkit for the Python programming language that works like a wrapper to the wxWindows C library. It is written in Python and uses the LPGL license. wxPython is a relatively fast cross-platform toolkit, and maybe it hasn't become the standard Python GUI yet because Tkinter is more portable. As a matter of fact, wxPython is the second most common GUI, coming just after Tkinter. Currently only Win32 and UNIX-like systems with GTK are supported. There are plans to support...

Info Bjn PythonTutorial

Mon, 13 Feb 2012 00:22:59 GMT

pay input 'How much were you paid this week 1 print 'I will deposit that into your account.' savings.deposit pay cash input 'How much would you like to withdraw 1 print 'I will withdraw that from your account.' savings.withdraw cash Display the balance. print savings Program Output with input shown in bold Enter your starting balance 1000.00 F.nter How much were you paid this week 50C.0f filter I will deposit that into your account. ' from y lt The account balance is i gt juu.ao. The name of...

REST Quick Start Finding Bargains on Amazoncom BeginningPython

Thu, 09 Feb 2012 05:24:54 GMT

Amazon.com, the popular online store, makes much of its data available through a REST web service called Amazon Web Services. Perhaps the most interesting feature of this web service is the capability it offers to search for books or other items and then retrieve metadata, pictures, and reviews for an item. Amazon effectively gives you programmatic access to its product database, something that would be difficult to duplicate or obtain by other means. The Amazon Web Services homepage is at http...

What is a pipe Learning to Program in Python

Wed, 08 Feb 2012 16:20:35 GMT

Conceptually a pipe can be thought of much like a hose-pipe, in that it is a conduit where we pour data in at one end and it flows out at the other. A pipe looks a lot like a file in that it is treated as a sequential data stream. Unlike a file, a pipe has two ends, so when we create a pipe we get two end points back in return. We can write to one end point and read from the other. Also unlike a file, there is no physical storage of data when we close a pipe, anything that was written in one...

Faking files Python Object Oriented Programming

Wed, 08 Feb 2012 06:48:47 GMT

Sometimes we need code that provides a file-like interface but doesn't actually read from or write to any real files. For example, we might want to retrieve a string from a third-party library that only knows how to write to a file. This is an example of the adapter pattern in action we need an adapter that converts the file-like interface into a string-like one. Two such adapters already exist in the standard library, Stringio and Bytesio. They behave in much the same way, except that one...

Review Questions Ljq PythonTutorial

Sat, 04 Feb 2012 22:49:51 GMT

1. This term refers to an individual item in a list. 2. This is a number that identifies a character in a string, or an item in a list. 3. This is the first index in a string or a list. d. The size of the list minus one 4. This is the last index in a string or a list. d. The size of the string or list minus one 5. This will happen if you try to use an index that is out of range for a list. a. a ValueError exception will occur b. an IndexError exception will occur c. The string or list will be...

How do I create a popup menu wxPython

Sat, 04 Feb 2012 12:51:52 GMT

Menus don't just pull down from menu bars at the top of your frame. They can also pop up from anywhere in the frame. Most of the time, a pop-up menu is used to provide actions that are context-sensitive, and that relate to the object at the location where the user clicks. Figure 10.6 displays an example of pop-up menus in action. Pop-up menus are created very similarly to standard menus, however, they are not attached to the menu bar. Listing 10.9 displays the code for a sample popup menu....

Ellipsis Object PythonReference

Fri, 03 Feb 2012 08:49:20 GMT

The Ellipsis object is used to indicate the presence of an ellipsis in an index lookup .There is a single object of this type, accessed through the built-in name Ellipsis. It has no attributes and evaluates as True. None of Python's built-in types make use of Ellipsis, but it may be useful if you are trying to build advanced functionality into the indexing operator on your own objects.The following code shows how an Ellipsis gets created and passed into the indexing operator e 3, , 4 Calls...

Info Fno PythonTutorial

Thu, 02 Feb 2012 16:56:37 GMT

The show-interest function displays the amount of 10 simple interest for a given principal, interest rate per period, and number of periods. def show_interest principal, rate, periods interest principal rate periods print 'The simple interest will be .2f.' interest The simple interest will be 1000.00. Notice in line 7 that the order of the keyword arguments does not match the order cf the parameters in the function header in line 13. Because a keyword argument specifies which parameter the...

How can I perform a print preview wxPython

Thu, 02 Feb 2012 13:44:43 GMT

One of the advantages of the device contexts as they are implemented in wxPy-thon is that it makes it easy to manage print preview, since most of the functionality comes from just replacing the printer device context with a screen device context. However, the print preview API is a bit different than for regular printing. For one thing, since print preview takes place on screen in a window, wxPy-thon provides a frame class for previewing. The next three sections describe the print preview...

Cropping and resizing images PythonComponents

Thu, 02 Feb 2012 09:59:41 GMT

The crop left, top, right, bottom method returns a rectangle portion of an image. resize w, h , filter returns a resized copy of an image. The filter argument controls what sort of sampling is used against the original image, and can be one of BILINEAR, BICUBIC, or NEAREST the default . One other useful method is thumbnail w, h , which resizes the object in place while maintaining the original aspect width-to-height ratio. Because of this, it may not use the exact size you pass in.

Web Services CherryPyGuide

Wed, 01 Feb 2012 14:11:09 GMT

In Chapter 5, we defined the data access layer and the entities our application would manipulate. In this chapter, we will explain how we can articulate our photoblog application by using web services as an API to access and operate the entities we have defined. We will introduce the concept of web services based on the REST principles as well as the Atom Publishing Protocol and explain how we can implement them using CherryPy. By the end of this chapter, you should understand how web services...

Say Hello Web2py

Wed, 01 Feb 2012 10:59:50 GMT

Here, as an example, we create a simple web app that displays the message Hello from MyApp to the user. We will call this application myapp. We will also add a counter that counts how many times the same user visits the page. You can create a new application simply by typing its name in the form on the top right of the site page in admin. After you press submit , the application is created as a copy of the built-in welcome application. Now you have a copy of the welcome application. To edit an...

Handling File Actions PyQtProgramming

Sun, 29 Jan 2012 23:49:57 GMT

The File menu is probably the most widely implemented menu in main-window-style applications, and in most cases it offers, at the least, new, save, and quit or exit options. dialog newimagedlg.NewImageDlg self if dialog.exec_ self.addRecentFile self.filename self.image QImage for action, check in self.resetableActions action.setChecked check self.image dialog.image self.filename None self.dirty True self.showImage self.sizeLabel.setText d x d self.image.width , self.image.height...

Using and bytearray Objects Python Object Oriented Programming

Sun, 29 Jan 2012 07:25:21 GMT

So far we've focused on str and bytes, since they subsume Python 2's unicode and str. Python 3.0 has a third string type, though bytearray, a mutable sequence of integers in the range 0 through 255, is essentially a mutable variant of bytes. As such, it supports the same string methods and sequence operations as bytes, as well as many of the mutable in-place-change operations supported by lists. The bytearray type is also available in Python 2.6 as a back-port from 3.0, but it does not enforce...

The Tkinter Module PythonIntroduction

Thu, 26 Jan 2012 21:27:34 GMT

Tkinter is Python's de facto standard GUI toolkit. It's the most cross-platform GUI. Many applications are written using Tkinter because it is a very powerful and flexible tool. Maybe the most notable features are its geometry management, which is much better than standard windows, and its efficient Text and Canvas widgets. Many toolkits support as good as or better geometry management some of them are listed in this chapter . Tkinter, which stands for Tk interface, is the standard Python...

The Team Repository View Agile Python Development

Thu, 26 Jan 2012 13:36:55 GMT

The team repository view supplants most of the Subversion status operations we looked at earlier in the chapter. It shows how the repository is different from your working copy, and how your working copy is different from the repository. It can combine those views showing all changes, or it can show only files with conflicts. It can show the aggregate changes, or it can break the differences down by revision. Open the repository view by choosing the menu item Window gt Open View gt Other. This...

Exercises Brv Python Interface Design

Thu, 26 Jan 2012 01:36:25 GMT

Exercise 9.7 This question is based on a Puzzler that was broadcast on the radio program Car Talk2 Give me a word with three consecutive double letters. I'll give you a couple of words that almost qualify, but don't. For example, the word committee, c-o-m-m-i-t-t-e-e. It would be great except for the 'i' that sneaks in there. Or Mississippi M-i-s-s-i-s-s-i-p-p-i. If you could take out those i's it would work. But there is a word that has three consecutive pairs of letters and to the best of my...

Options specific to Canvas Python Tkinter Programming

Wed, 25 Jan 2012 16:21:27 GMT

closeenough Specifies a floating-point value indicating how float 0.5 close the mouse cursor must be to an item before it is considered to be inside the item. Defaults to 1.0. confine Specifies a boolean value that indicates whether or not it should be allowable to set the canvas's view outside the region defined by the scrollre-gion argument. Defaults to true, which means that the view will be constrained within the scroll region. Specifies the color to use as background in the color 'yel-...

Distributing Unix applications Python Tkinter Programming

Wed, 25 Jan 2012 15:46:44 GMT

Supporting your application is usually a simple task once you have access to a built Python and Tcl Tk. In general, UNIX end users are capable of building and installing both of these so you may be able to simply require your end users to take care of them. Then your application installation may be as simple as extracting files from a tar file and editing the users' environments appropriately. For the moment, let's assume that this is the case, so we will concentrate on getting your application...

Figure The flat plane becomes a full rotating cube Python Lua And Ruby

Wed, 25 Jan 2012 09:00:57 GMT

Let's say you wanted to speed up and twist your rotating cube around a bit more. It's easy to fiddle with MatrixMode, especially since you've thought ahead and included a number of variables with which to do it x,y, and z rots are the rotations on each axis xrot yrot zrot 0.0 These variables, xrot, yrot, and zrot, can be used to rotate the cube in a new way on the x-, y-, and x-axes. Do so by adding a few lines to the top of drawgraphics glLoadidentity glTranslatef 0.0, 0.0, -5.0 global rquad...

The String Data Type PythonProgramming

Wed, 25 Jan 2012 03:57:52 GMT

A string is a sequence of characters. In Chapter 2 you learned that a string literal is a sequence of characters in quotations. Python also allows strings to be delimited by single quotes apostrophes . There's no difference just be sure to use a matching set. Strings can be stored in variables, just like numbers. Here are some examples illustrating these two forms of string literals. gt gt gt strl Hello gt gt gt str2 'spam' gt gt gt print strl, str2 Hello spam gt gt gt type strl lt type...

The Address Book as ClientServer Learning to Program in Python

Tue, 24 Jan 2012 19:57:55 GMT

Back in the files topic we built a version of our address book using a dictionary. Let's reuse that example but this time we will build a client server version. Notice that the original code broke one of the good practice rules we discussed earlier I included User Interface code in my helper functions. If we were to try to use this code we would get messages from the child process mixed up with messages from the parent. We need to tweak the code slightly so that we can turn it into a reusable...

Firststep changes PythonNumpy

Tue, 24 Jan 2012 16:20:12 GMT

In order to use the compatibility layer there are still a few changes that need to be made to your code. Many of these changes can be made by running the alter_codel module with your code as input. 1. Importing the alter_codel module handles all these changes a import Numeric - gt import numpy.oldnumeric as Numeric b import Numeric as XX - gt import numpy.oldnumeric as XX c from Numeric import lt name1 gt , lt nameN gt - gt from numpy.oldnumeric import lt name1 gt , , lt nameN gt d from Numeric...

Example AppleScript interface running on Mac MobilePython

Mon, 23 Jan 2012 19:56:03 GMT

ALLOWED_SCRIPTS edit ser serial.Serial ' dev tty.pybook' print Waiting for message while True msg serial.readline .strip if msg exit print gt gt serial, bye break print Running script msg os.system osascript s.script msg print gt gt serial, Script ok The idea is that the phone client is used to choose one of the scripts to execute on the PC side. Once again, we can use Example 59 as the phone client. Again, echoing should be disabled by setting ECHO False in the client. In Python, the os.system...

r b Axq Engineering with Python

Sun, 22 Jan 2012 23:01:39 GMT

s0 r0 lacking a previous search direction, choose the direction of steepest descent if rk 11 lt e exit loop e is the error tolerance It can be shown that the residual vectors r1, r2, r3, produced by the algorithm are mutually orthogonal, that is, ri r,- 0, i j. Now suppose that we have carried out enough iterations to have computed the whole set of n residual vectors. The residual resulting from the next iteration must be a null vector rn 1 0 , indicating that the solution has been obtained. It...

generateusernamespy Python Programming Techniques

Sat, 21 Jan 2012 20:52:15 GMT

Imagine we are setting up a new computer system and need to generate user-names for all of our organization's staff. We have a plain text data file UTF-8 encoding where each line represents a record and fields are colon-delimited. Each record concerns one member of the staff and the fields are their unique staff ID, forename, middle name which may be an empty field , surname, and department name. Here is an extract of a few lines from an example data users.txt data file 1601 Albert Lukas...

Info Fgj PythonTutorial

Sat, 21 Jan 2012 02:17:14 GMT

This program opens the file in line 6, and then in line 10 reads the first field of the first record. This will be the first employee's name. The while l oop in line 13 tests the value to determine whether it is an empty string. If it is not, then the loop iterates. Inside the loop, the program reads the record's second and third fields the employee's ID number and department , and displays them. Then, in line 32 the first field of the next record the next employee's name is read. The loop...

Indexing Lists Versus Dictionaries Python Language Processing

Thu, 19 Jan 2012 22:37:48 GMT

A text, as we have seen, is treated in Python as a list of words. An important property of lists is that we can look up a particular item by giving its index, e.g., textl l00 . Notice how we specify a number and get back a word. We can think of a list as a simple kind of table, as shown in Figure 5-2. Figure 5-2. List lookup We access the contents of a Python list with the help of an integer index. Contrast this situation with frequency distributions Section 1.3 , where we specify a word and...

Examples 1 MobilePython

Wed, 18 Jan 2012 11:23:35 GMT

Hangman server 2 3 Hangman server 3 3 Text to speech MP3 player Blocking MP3 player MIDI player Sound recorder Animal sounds Binding a keycode to a callback function Key events Creating a directory for application data Retrieve the current GSM cell ID GSM location application 56 Send photos to another phone via Bluetooth 60 PySerial script running on PC 61 AppleScript interface running on Mac 72 Set the default access point SMS search using list comprehensions Input sanitization using list...

Understanding the application object lifecycle wxPython

Wed, 18 Jan 2012 09:18:40 GMT

The lifecycle of your wxPython application object begins when the application instance is created and ends just after the last application window is closed. This does not necessarily correspond to the beginning and ending of the Python script that surrounds your wxPython application. The script may choose to do some activity before creating the wxPython application, and may do further cleanup after the application MainLoop exits. All wxPython activity, however, must be performed during the life...

escape Jython

Wed, 18 Jan 2012 08:47:49 GMT

escape escapes all nonalphanumeric characters before passing the expression to tee compiler, and returns a string with all metacharacters escaped. Here's an example in wficF the compile function fails because there are unmatched parentykses gt gt gt from re import gt gt gt strVar group gt gt gt cre compile strVar File lt console gt , line 1, in re.error Unmatched parentheses. In this example, tfe non-alphanumeric characters are escaped, so tfe compile function works gt gt gt cre compile escape...

Understanding Environment variables IronPythonTutorial

Wed, 18 Jan 2012 08:42:47 GMT

Environment variables are simply a kind of storage location managed by the operating system. When you open a command prompt, you can see a list of environment variables by typing Set and pressing Enter. Figure 10-6 shows the environment variables on my system. The environment variables or at least their values will differ on your machine, so you should take a look at them. If you want to see the value of a particular environment variable, type Set VariableName such as Set USERNAME and press...

Filtering PythonVisualization

Wed, 18 Jan 2012 06:14:55 GMT

One of the reasons to transform a time-domain signal to a frequency-domain signal is for the purpose of filtering. A filter is an operation that changes a signal. Much like filters in your kitchen sink, filters let some frequencies pass water , while stopping other frequencies large food remains . Filters are used in a variety of applications, ranging from audio to radar systems. Filters are categorized by their behavior. A filter that lets through low frequencies and stops high frequencies is...

Info Nmd PythonTutorial

Wed, 18 Jan 2012 03:41:46 GMT

F is rhe Fahrenheit temperature and C is the Celsius temperature. A county collects property taxes on the assessment value of property, which is 60 percent of the property's actual value. If an acre of land is valued at 10,000, its assessment value is 6,000. The property tax is then 0.64 for each 100 of the assessment value. The tax for the acre assessed at 6,000 will be 38.40. Write a GUI program that displays the assessment value and property rax when a user enters the actual value of a...

Defining Your Own Modules Python Computer Science

Wed, 18 Jan 2012 02:03:57 GMT

Section 2.1, The Big Picture, on page 17 explained that in order to save code for later use, you can put it in a file with a .py extension. You can then tell Python to run the code in that file, rather than typing commands in at the interactive prompt. What we didn't tell you then is that every Python file can be used as a module. The name of the module is the same as the name of the file, but without the .py extension. For example, the following function is taken from Section 2.6, Function...

Reading Tagged Corpora Python Language Processing

Tue, 17 Jan 2012 22:06:40 GMT

Several of the corpora included with NLTK have been tagged for their part-of-speech. Here's an example of what you might see if you opened a file from the Brown Corpus with a text editor The at Fulton np-tl County nn-tl Grand jj-tl Jury nn-tl said vbd Friday nr an at inves-tigation nn of in Atlanta's np recent jj primary nn election nn produced vbd no at evidence nn '' '' that cs any dti irregularities nns took vbd place nn . . Other corpora use a variety of formats for storing part-of-speech...

Formulating Algorithms Case Study CounterControlled Repetition PythonXML

Tue, 17 Jan 2012 17:28:47 GMT

To illustrate how algorithms are developed, we solve several variations of a class-averaging problem. Consider the following problem statement A class often students took a quiz. The grades integers in the range 0 -100 for this quiz are available. Determine the class average on the quiz. The class average is equal to the sum of the grades divided by the number of students. The algorithm for solving this problem requests each of the grades, performs the averaging calculation and prints the...

Not all snakes will squish you PythonLearning

Tue, 17 Jan 2012 16:52:24 GMT

Chances are you were given this book for your birthday. Or possibly for Christmas. Aunty Mildred was going to give you mismatching socks that were two sizes too large and you wouldn't want to wear when you grew into them anyway . Instead, she heard someone talking about this printable book, remembered you had one of those computer-thingamabobs that you tried to show her how to use last Christmas you gave up when she started trying to talk into the mouse , and got them to print another copy....

The XPath Access Mechanism XMLProcessing

Tue, 17 Jan 2012 16:43:12 GMT

The XPath part of the solution makes accessing the elements within the XML document much easier than a traditional event-driven or even DOM-based parser. To use the XPath interface is simplicity itself. For example, to get a list of all the subelements, you need to do is access the elements property of the parent element. The each method accepts an XPath definition that in turn returns a list of all the subelements that it finds. For example, you can work through all the items using this...

The ACalculus Python Language Processing

Tue, 17 Jan 2012 15:04:47 GMT

In Section 1.3, we pointed out that mathematical set notation was a helpful method of specifying properties P of words that we wanted to select from a document. We illustrated this with 31 , which we glossed as the set of all w such that w is an element of V the vocabulary and w has property P. It turns out to be extremely useful to add something to first-order logic that will achieve the same effect. We do this with the A-operator pronounced lambda . The A counterpart to 31 is 32 . Since we...

The Netbeans Python Debugger JythonGuide

Tue, 17 Jan 2012 14:01:45 GMT

As mentioned previously, the Netbeans IDE also includes a Python debugger that is derived from JeanYves Mengant's jpydbg debugger. This section will discuss how to make use of the Netbeans Python debugger along with some examples using our HockeyRoster code that was written in the previous section. If you have used a debugger in another IDE, or perhaps the Java debugger that is available for Netbeans, this debugger will feel quite familiar. The Python debugger includes many features such as...

Example Plain Text Table of Contents Python Coding Techniques

Tue, 17 Jan 2012 13:09:22 GMT

Though there are many forms of documentation, plain text is perhaps the most common, as it doesn't require any additional software to view. Navigating large chunks of documentation can be difficult, though, because of the lack of links or page numbers for a table of contents. Line numbers could be used instead of page numbers, but a properly formatted table of contents can still be tedious to maintain. Consider a typical table of contents, where the title of a section is left-aligned and the...

Unpacking arguments Python Object Oriented Programming

Tue, 17 Jan 2012 10:51:28 GMT

There's one more nifty trick involving variable arguments and keyword arguments. We've used it in some of our previous examples, but it's never too late for an explanation. Given a list or dictionary of values, we can pass those values into a function as if they were normal positional or keyword arguments. Have a look at this code def show_args arg1, arg2, arg3 THREE print arg1, arg2, arg3 arg1 ONE, arg2 TWO print Unpacking a sequence , end show_args some_args print Unpacking a dict , end...

Asynchronous IO with select and poll BeginningPython

Tue, 17 Jan 2012 10:51:04 GMT

When a server communicates with a client, the data it receives from the client may come in fits and spurts. If you're using forking and threading, that's not a problem. While one parallel waits for data, other parallels may continue dealing with their own clients. Another way to go, however, is to deal only with the clients that actually have something to say at a given moment. You don't even have to hear them out you just hear or, rather, read a little, and then put it back in line with the...

Deploying a Single JAR JythonGuide

Tue, 17 Jan 2012 10:39:38 GMT

In order to deploy an application to the Java Warehouse, it must be packaged as a single JAR file. We've already discussed packaging Jython applications into a JAR file using the Jython standalone method in Chapter 13. In this section, you will learn how to make use of the One-JAR http one-jar.sourceforge.net product to distribute client-based Jython applications. In order to get started, you will need to grab a copy of One-JAR. There are a few options available on the download site, but for...

A completely different way to set up variables Python Object Oriented Programming

Tue, 17 Jan 2012 10:23:19 GMT

One of the most common uses for the various setup and teardown functions is to ensure certain class or module variables are available with a known value before each test method is run. py.test offers a completely different way to do this using what are known as funcargs, short for function arguments. Funcargs are basically named variables that are previously set up in a test configuration file. This allows us to separate configuration from execution of tests, and allows the funcargs to be used...

Python DB API PythonIntroduction

Tue, 17 Jan 2012 09:26:05 GMT

The quest to provide a standard way to interface to database systems drove a group of people to develop Python Database API. The Python DB API is maintained by the Database Special Interest Group DB-SIG . For more information, check out their Web site at http www.python.org sigs db-sig . The following list shows all the database modules that currently implement the Python DB API specification proposed by the DB-SIG. This means that after you understand the API, you will be able to handle, in a...

Implementing the Singleton Design Pattern IronPythonDevelopment

Tue, 17 Jan 2012 08:47:00 GMT

Sometimes in your applications you will have objects that by their very nature should exist at most one time and one time only a global application object would be one example. Indeed, Singletons occasionally get a bad rap for being glorified global variables, which developers frown on because it's more of a hassle to ensure that the state of that variable is correct everywhere. In IronPython, we'll store an instance of a class in a variable for reference if that instance variable is null, we...

Basic Concepts PythonReference

Tue, 17 Jan 2012 08:39:25 GMT

A running program is called a process. Each process has its own system state, which includes memory, lists of open files, a program counter that keeps track of the instruction being executed, and a call stack used to hold the local variables of functions. Normally, a process executes statements one after the other in a single sequence of control flow, which is sometimes called the main thread of the process. At any given time, the program is only doing one thing. A program can create new...

Embedding the Jython Interpreter BeginningPython

Tue, 17 Jan 2012 07:16:42 GMT

By embedding the Jython interpreter in your own Java classes, you can run scripts from within your application, gaining control over the complete environment. That's important because few Java applications run from the command line. You can find the Jython interpreter in the class org.python.util.PythonInterpreter. You can use code like the following to initialize the Jython interpreter Properties props new Properties props.put python.home, pythonHome PythonInterpreter.initialize...

Working with Surface Objects Pygame Game Development

Tue, 17 Jan 2012 05:20:27 GMT

Loading images into Pygame is done with a simple one-liner pygame.image.load takes the file name of the image you want to load and returns a surface object, which is a container for an image. Surfaces can represent many types of image, but Pygame hides most of these details from us so we can treat them in much the same way. Once you have a surface in memory, you can draw on it, transform it, or copy it to another surface to build up an image. Even the screen is represented as a surface object....

Computing Probabilities Python Scientific Programming

Tue, 17 Jan 2012 04:22:00 GMT

With the mathematical rules from probability theory one may compute the probability that a certain event happens, say the probability that you get one black ball when drawing three balls from a hat with four black balls, six white balls, and three green balls. Unfortunately, theoretical calculations of probabilities may soon become hard or impossible if the problem is slightly changed. There is a simple numerical way of computing probabilities that is generally applicable to problems with...

Info Qxj PythonTutorial

Tue, 17 Jan 2012 04:12:40 GMT

Notice that the__init__method has two parameter variables self and bal. The bal parameter will accept the account's starting balance as an argument. In line 10 the bal parameter amount is assigned to the object's__balance attribute. The deposit method is in lines 15 through 16. This method has two parameter variables self and amount. When the method is called, the amount that is to be deposited into the account is passed into the amount parameter. The value of the parameter is then added to...

Event Binding 1 Tkinter

Mon, 16 Jan 2012 23:18:18 GMT

Happily, lambda also gives us a way to parameterize event binding. Instead of self.buttonHandler a event, button name, 1, Good stuff which wouldn't work, because there was no way to include the event argument in the argument list , we can use lambda, this way event binding -- passing the event as an argument self.button1.bind , event, arg1 button name, arg2 1, arg3 Good stuff self.buttonHandler a event, arg1, arg2, arg3 Note that event here is a variable name -- it is not a Python keyword or...

Using the interactive interpreter IronPythonIntroduction

Mon, 16 Jan 2012 21:45:32 GMT

When you download IronPython,33 you have two choices. You can download and install the msi installer IronPython 2 only , which includes the Python 2.5 standard library. Alternately, you can download and unpack the binary distribution that comes as a zip file. Whichever route you take, you'll have two executables, ipy.exe and ipyw.exe, which are the equivalents of the Python executables python.exe and pythonw.exe. Both are used to launch Python scripts ipy.exe launches them with a console...

A TextBased UI PythonProgramming

Mon, 16 Jan 2012 21:34:44 GMT

In designing PokerApp we have also developed a specification for a generic Pokerlnterface class. Our interface must support the methods for displaying information setMoney, setDice, and showResult. It must also have methods that allow for input from the user wantToPlay, and chooseDice. These methods can be implemented in many different ways, producing programs that look quite different even though the underlying model, PokerApp, remains the same. Usually, graphical interfaces are much more...

The SOAP Response BeginningPython

Mon, 16 Jan 2012 21:18:23 GMT

Here's a possible response you might get from a SOAP server after sending it the sortList request lt xml version 1.1 encoding UTF-8 gt lt SOAP-ENV Envelope encoding lt SOAP-ENV Body lt lt ns1 sortList xmlns ns1 urn SearchSort lt lt tem gt 10 lt item gt lt return lt lt lt ns1 sortList gt lt lt SOAP-ENV Envelope gt Just as with XML-RPC, a SOAP response has the same basic structure as a SOAP request. Where the SOAP request had a list of arguments, the SOAP response has a single return value. This,...

Expressions functions and Python types IronPythonIntroduction

Mon, 16 Jan 2012 20:03:43 GMT

The simplest example of this is to use IronPython to evaluate individual expressions. IronPython makes a great calculator 21 So far, whenever we have executed Python code from a string we have passed in the enumeration member SourceCodeKind.Statements. This member has a sister, SourceCodeKind.Expression, that allows us to evaluate an expression and return an object. It is used in this snippet of C to evaluate a simple mathematical expression string code 2 3 5 ScriptSource source 21 You can see...

Human factors Python Tkinter Programming

Mon, 16 Jan 2012 19:47:39 GMT

Extensive documents on Human Factor Engineering describe GUI design in scientific terms see the Reference section . In particular, font choice may be based on calculating the arc subtended by a character from a point 20 inches from the character the viewing position . While I have worked on projects where it was necessary to actually measure these angles to confirm compliance with specifications, it is not usually necessary to be so precise. When designing an application that includes a GUI,...

using Early Binding IronPythonTutorial

Mon, 16 Jan 2012 19:37:42 GMT

As previously mentioned, using early binding means creating a reference to the COM component and then using that reference to interact with the component. IronPython doesn't support the standard methods of early binding that you might have used in other languages. What you do instead is create an interoperability DLL and then import that DLL into your application. The Defining an Interop DLL section of the chapter describes this process in considerably more detail. Early binding provides the...

NLTKs Regular Expression Tokenizer Python Language Processing

Mon, 16 Jan 2012 17:37:37 GMT

The function nltk.regexp_tokenize is similar to re.findall as we've been using it for tokenization . However, nltk.regexp_tokenize is more efficient for this task, and avoids the need for special treatment of parentheses. For readability we break up the regular expression over several lines and add a comment about each line. The special x verbose flag tells Python to strip out the embedded whitespace and comments. gt gt gt text 'That U.S.A. poster-print costs 12.40 ' gt gt gt pattern r''' x set...

How do I manage the row and column headers of a grid wxPython

Mon, 16 Jan 2012 16:32:10 GMT

In a wxPython grid control, each row and column has its own label. By default, rows are given numeric labels starting with 1 and columns are given alphabetical labels starting with A and continuing to Z, which is followed by aa, ab, and so on. If you're creating a spreadsheet, this is great, but not necessary for most other applications. For something a bit less generic, wxPython provides methods to change the labels. Figure 14.3 displays a sample grid with label headers. Figure 14.3 A sample...

Python datatypes IronPythonIntroduction

Mon, 16 Jan 2012 16:07:16 GMT

Python boasts a rich set of built-in datatypes that you can use without importing any modules. Most of these, with the exception of the set that we introduce shortly, have syntax for including them within your code. To understand the examples in this book or to write Python yourself, you're going to need to recognize them. Table 2.1 contains a guide to all the basic datatypes and their syntaxes. Table 2.1 The built-in datatypes and their syntaxes Table 2.1 The built-in datatypes and their...

Instead of using the command line interpreter you can also use a graphical user interface called IDLE see Figure PythonIntroduction

Mon, 16 Jan 2012 15:43:09 GMT

Figure 2.3. idle is Python's GUI interpreter. python 1.5.2 C cip Apr 13 1999, 10 51 12 msc 3 2 bit lintel on Copyright 1 amp 91-199E Stichting Mattieinatisen Centrum, Ainscertfani See Chapter 16, Development Environment, for details about using IDLE. As you can see by looking at the coding area in both Figures 2.2 and 2.3, the interpreter's primary prompt is a gt gt gt . Let's start interacting with Python by running a variation of the standard hello world program. gt gt gt print Hello Python...

Solution Esb Python Solutions to problems

Mon, 16 Jan 2012 13:50:14 GMT

Perhaps you can do better, if the sequence is big, has been shuffled enough, and comparisons between its items are costly. Sort is very fast, but in the end when applied to a thoroughly shuffled sequence of length n it always takes o n log n time, while there exist algorithms that can be used to get the nth smallest element in time o n . Here is a function with a solid implementation of such an algorithm Find the nth rank ordered element the least value has rank 0 . make a new list, deal with...

Modeling the real world PythonProgramming

Mon, 16 Jan 2012 13:31:05 GMT

There are many reasons to use a computer to simulate or model the real world. Sometimes it isn't practical to do an experiment because of time, distance, danger, or other reasons. For example, in the last chapter we simulated flipping a coin a million times. Most of us don't have time to do that with a real coin, but a computer simulation did it in seconds. Sometimes scientists want to figure out What if . . . What if an asteroid smashed into the moon We can't make a real asteroid smash into...

Redirecting output wxPython

Mon, 16 Jan 2012 12:48:08 GMT

If wxPython is controlling the standard streams, then text sent to the streams via any mechanism including a print statement or a system traceback is redirected to a separate wxPython frame. Text sent to the streams before the wxPython application begins or after it ends is, of course, processed normally. Listing 2.1, demonstrates both the application lifecycle and the stdout stderr redirection. Listing 2.1 A sample startup script showing output stream redirection def _init_ self, parent, id,...

PyArrayMultiIterType PythonNumpy

Mon, 16 Jan 2012 11:13:51 GMT

This type provides an iterator that encapsulates the concept of broadcasting. It allows N arrays to be broadcast together so that the loop progresses in C-style contiguous fashion over the broadcasted array. The corresponding C-structure is the PyArrayMultilterObj ect whose memory layout must begin any object, obj, passed in to the PyArray_Broadcast obj function. Broadcasting is performed by adjusting array iterators so that each iterator represents the broadcasted shape and size, but has its...

A Quick Introduction to PyParsing Python Programming Techniques

Mon, 16 Jan 2012 10:34:28 GMT

PyParsing makes no real distinction between lexing and parsing. Instead, it provides functions and classes to create parser elements one element for each thing to be matched. Some parser elements are provided predefined by PyParsing, others can be created by calling PyParsing functions or by instantiating PyParsing classes. Parser elements can also be created by combining other parser elements together for example, concatenating them with to form a sequence of parser elements, or or-ing them...

Chapter Summary Hmv Python Object Oriented Programming

Mon, 16 Jan 2012 10:07:31 GMT

In this chapter, we covered the basics of modules, attributes, and imports and explored the operation of import statements. We learned that imports find the designated file on the module search path, compile it to byte code, and execute all of its statements to generate its contents. We also learned how to configure the search path to be able to import from directories other than the home directory and the standard library directories, primarily with PYTHONPATH settings. As this chapter...

Tcl and Unicode XMLProcessing

Mon, 16 Jan 2012 09:18:46 GMT

The TclXML parser will read Unicode encoded documents directly, so you need to identify or display either entities or character data. Then you will need to be able to translate between Unicode formats. Tcl 8.1 and after includes the encoding command, which will convert strings between the different encoding formats for you. See the following sidebar for information on determining which encodings are supported by your system. To determine which encodings are supported by your Tcl installation,...

Description Slg PythonReference

Mon, 16 Jan 2012 08:22:36 GMT

Maximum length of a filename in a directory. Indicates whether an attempt to create a file with a name longer than pc_name_max for a directory will fail with an Maximum length of a relative path name when the directory fd is the current working directory. Size of the pipe buffer when fd refers to a pipe or FIFO. Indicates whether priority I O can be performed on fd. Indicates whether synchronous I O can be performed on fd. Indicates whether fd allows special-character processing to be disabled....

Troubleshooting Jython

Mon, 16 Jan 2012 07:48:47 GMT

If you don't see the okay message, type c j2skd1.4.0 bin java at the DOS prompt C gt c j2sjd1.4.0 bin java -version java version 1.3.0 Java TM 2 Runtime Environment, Standard Edition build 1.4.0-b92 Java HotSpot TM Client VM build 1.4.0-b92, mixed mode If this works, you have a problem with your PATH statement. Try entering PATH at the command line to see what it looks like. Probably you have a lyho or you forgot to reboot autoexec. bat runs only after rebooting . If you still don't see the...

Summary Uat Python Computer Science

Mon, 16 Jan 2012 05:32:50 GMT

In this chapter, we learned the following A module is a collection of functions and variables grouped together in a file. To use a module, you must first import it. After it has been imported, you refer to its contents using modulename. thingname. Put docstrings at the start of modules or functions to describe their contents and use. Every thing in a Python program is an object. Objects have methods, which work just like functions but are associated with the object's type. Methods are called...

Handling Help Actions PyQtProgramming

Sun, 15 Jan 2012 23:21:01 GMT

When we created the main window's actions, we provided each with help text, and set it as their status text and as their tooltip text. This means that when the user navigates the application's menu system, the status text of the currently highlighted menu option will automatically appear in the status bar. Similarly, if the user hovers the mouse over a toolbar button, the corresponding tooltip text will be displayed in a tooltip. For an application as small and simple as the Image Changer,...

Info Ffc PythonTutorial

Sun, 15 Jan 2012 22:43:38 GMT

The program should ask the user to enter a temperature in Celsius, and then display the temperature converted to Fahrenheit. Last month Joe purchased some stock in Acme Software, inc. Here are the derails of the purchase The number of shares that Joe purchased was 1,000. When Joe purchased the stock, he paid 32.87 per share. Joe paid his stockbroker a commission that amounted to 2 percent of the amount he paid for the stock. Two weeks later Joe sold the stock. Here are the details of the sale...

Annotating the Graph PythonVisualization

Sun, 15 Jan 2012 20:20:01 GMT

We'd like to add some more information to the GPS graph we'd like to know where we've stopped and where we were speeding. For this we use the function find , which is part of the PyLab package. find returns an array of indices that satisfy the condition, in our case gt STANDING_KMH 10.0 gt SPEEDING_KMH 50.0 gt Istand find v lt STANDING_KMH gt Ispeed find v gt SPEEDING_KMH gt Icruise find v gt STANDING_KMH amp v lt SPEEDING_KMH We also calculate when we're cruising i.e., not speeding nor...

PyInotify Python for Linux System

Sun, 15 Jan 2012 19:37:32 GMT

If you have the privilege of working with GNU Linux platforms, then you will appreciate PyInotify. According to the documentation, it is a Python module for watching filesystem changes. The official project page is here http pyinotify.sourceforge.net. Example 8-9 shows how it could work. Example 8-9. Event-monitoring Pyinotify script from pyinotify import WatchManager, Notifier, ProcessEvent, EventsCodes class PClose ProcessEvent Processes on close event def __init__ self, path self.path path...

Attributesfromarguments Python Solutions to problems

Sun, 15 Jan 2012 16:17:49 GMT

As long as no additional logic is in the body of__init__, the dict returned by calling the built- in function locals contains only the arguments that were passed to__init__ plus those arguments that were not passed but have default values . Function attributesFromDict extracts the object, relying on the convention that the object is always an argument named 'self', and then interprets all other items in the dictionary as names and values of attributes to set. A similar but simpler technique,...

Solution Vpy Python Solutions to problems

Sun, 15 Jan 2012 16:14:47 GMT

You need a factory function that catches the cases in which either the getter or the setter argument is a string, and wraps the appropriate argument into a function, then delegates the rest of the work to Python's built-in property def xproperty fget, fset, fdel None, doc None if isinstance fget, str attr_name fget def fget obj return getattr obj, attr_name elif isinstance fset, str attr_name fset def fset obj, val setattr obj, attr_name, val else raise TypeError, 'either fget or fset must be a...

Python Supertuple Python Solutions to problems

Sun, 15 Jan 2012 16:14:27 GMT

You often want to pass data around by means of tuples, which play the role of C's structs, or that of simple records in other languages. Having to remember which numeric index corresponds to which field, and accessing the fields by indexing, is often bothersome. Some Python Standard Library modules, such as time and os, which in old Python versions used to return tuples, have fixed the problem by returning, instead, instances of tuple-like types that let you access the fields by name, as...

Default Parameter Values Python Computer Science

Sun, 15 Jan 2012 16:08:19 GMT

Default parameter values are the first of these tools. Here's an example Download construct default_define.py def total values, start 0, end None '''Add up the values in a list. If none are given, the total is zero. If 'start' is not specified, start at the beginning. If 'end' is specified, go up to but not including that index otherwise, go to the end of the list. '' ' This function has three parameters a list of values and two indices that specify which part of the list to sum up. What makes...

Installing Twill PythonTesting

Sun, 15 Jan 2012 15:39:43 GMT

You can find Twill in the Python Package Index at http pypi.python.org pypi twill . At the time of writing, the latest version can be directly downloaded from Windows users will need to use an archiving program which understands Tar and GZip formats, such as 7-Zip http www.7-zip.org to extract the files. Once you have the files unpacked, you can install them by opening a command prompt, changing to the twill-0.9 directory, and running or, if you can't write to Python's site-packages directory,...

A nifty trick PythonTesting

Sun, 15 Jan 2012 14:14:35 GMT

If you're using Python 2.4 or greater, you can define a function decorator that makes it simple to write Twill tests as Python functions. from twill.parse import execute_string from twill.errors import TwillAssertionError def twill_test func execute_string func._doc_, no_reset False if args and hasattr args 0 , 'fail' If you put that code in a Python module here called twill_decorator and then import twill_test into your testing code, you can write Twill tests like so from unittest import...

What just happened Ehn PythonTesting

Sun, 15 Jan 2012 13:19:22 GMT

We used Twill to browse to slashdot.org, navigated into the Science section, searched for aardvark, and then checked to see if the resulting page contained the words aardvark and Elephant. Of what use it that We're not limited to goofing around on slashdot.org. We can use the Twill language to describe any interaction between a web browser and a web server. That means, we can use it to describe the expected behavior of our own web applications. If we can describe expected behavior, we can write...

Exercise Ovb PyQtProgramming

Sun, 15 Jan 2012 12:55:00 GMT

Use Qt Designer to create a user interface with one of the designs shown in Figure 7.11, or with a design of your own. You will probably need to use a Grid Layout, as well as Vertical and Horizontal Layouts. For grid layouts, you may have to try a few times, perhaps resizing and positioning widgets to help Qt Designer create the grid you want. Use QDialogButtonBoxes for the buttons. Figure 7.11 A dialog with two different designs Figure 7.11 A dialog with two different designs The price spinbox...

Exercises Python Computer Science

Sun, 15 Jan 2012 06:06:01 GMT

Here are some exercises for you to try on your own 1. For each of the following expressions, what value will the expression give Verify your answers by typing the expressions into Python. 2. Unary minus negates a number. Unary plus exists as well for example, Python understands 5. If x has the value -17, what do you think x should do Should it leave the sign of the number alone Should it act like absolute value, removing any negation Use the Python shell to find out its behavior. 3. a Create a...