How To Create Your Own Programming Language

Create Your Own Programming Language

Creating your first programming language is easier than you think. Want to create a programming language, but don't feel like going through one of those expensive and boring 1000 pages book ? Well, you're not alone . The best system to create your first programming language. The eBook. A 77 pages Pdf detailing core concepts and applying them to a custom language. (included: ePub & Mobi formats). Exercises & solutions. Proposed extensions to the language with solutions at the end of the book. Three languages. Full source code of three languages in Ruby & Java. Easy to extend and play with. A screencast. Explaining step by step how to extend the Jvm language. More here...

Create Your Own Programming Language Overview

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Highly Recommended

All of the information that the author discovered has been compiled into a downloadable book so that purchasers of Create Your Own Programming Language can begin putting the methods it teaches to use as soon as possible.

This ebook does what it says, and you can read all the claims at his official website. I highly recommend getting this book.

XML Solutions in Python

Python's XML support is probably one of the most complex of the different solutions available, largely because of the way in which the different XML parsers have been developed. The original XML parsing system provided with Python 1.5.2 is called xmllib, and it comes as standard with all Python distributions. xmllib was developed on the same basis as the sgm-llib module, which provides SGML parsing tools. The xmllib parser is both a simple validation parser and an event-driven data parser that...

Counting calories

Since everyone is concerned about nutrition these days, let's add a calorie count for each combination on the menu. You might not care about the calories, but I bet your parents do That will let us use some of Python's math abilities, which we learned about back in chapter 3. We already know which items are in each combination. All we need now are the calories for each item. Then we can add them all up in the innermost loop. Here's some code that sets how many calories are in each item Now we...

Images

Python Programming Madeleine

Now that we have seen the basic features of modules, objects, and methods, let's look at how they can solve real-world problems. For our running example, we will write some programs that display and manipulate pictures and other images. Suppose you have a file called pic207.jpg on your hard drive and want to display it on your screen. You could double-click to open it, but what does that actually do To start to answer that question, type the following into a Python prompt gt gt gt import media...

The Pareto Principle

In 1906, Italian economist Vilfredo Pareto noted that 80 of the wealth in Italy was held by just 20 of its citizens. In over a century since then, this idea has been put to the test in a number of fields beyond economics, and similar patterns have been found. The exact percentages may vary, but the general observation has emerged over time the vast majority of effects in many systems are a result of just a small number of the causes. In programming, this principle can manifest in a number of...

Last Month Joe Purchased Some Stock In Acme Software Inc.

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...

PyTree A Generic Tree Object Viewer

Python Object Oriented Canvas

Up to now, this chapter has been command-line-oriented. To wrap up, I want to show you a program that merges the GUI technology we studied earlier in the book with some of the data structure ideas we've met in this chapter. This program is called PyTree, a generic tree data structure viewer written in Python with the Tkinter GUI library. PyTree sketches out the nodes of a tree on screen as boxes connected by arrows. It also knows how to route mouseclicks on drawn tree nodes back to the tree, to...

Using nested loops

So what can we do with all these nested loops Well, one of the things they're good for is figuring out all the possible permutations and combinations of a series of decisions. Permutation is a mathematical term that means a unique way of combining a set of things. Combination means something very similar. The difference is that, with a combination, the order doesn't matter, but with a permutation, the order does matter. If I asked you to pick three numbers from 1 to 20, you could pick and so...

Simulation and Design

You may not realize it, but you have reached a significant milestone in the journey to becoming a computer scientist. You now have all the tools to write programs that solve interesting problems. By interesting, I mean problems that would be difficult or impossible to solve without the ability to write and implement computer algorithms. You are probably not yet ready to write the next great killer application, but you can do some nontrivial computing. One particularly powerful technique for...

Brute Force

However, while this cipher may fool some people who don't understand cryptography, it won't keep a message secret from someone who knows cryptanalysis. While cryptography is the science of making codes, cryptanalysis is the study of breaking codes. Do you wish to encrypt or decrypt a message encrypt The door key will be hidden under the mat until the fourth of July. Bpm lwwz smg eqtt jm pqllmv cvlmz bpm uib cvbqt bpm nwczbp wn Rctg. The whole point of...

Remove pages OK and Cancel dialog box

When the user asks to perform an irreversible action, such as removing a tab page, it's normal to ask for confirmation of the action. You're undoubtedly familiar with the standard Windows OK Cancel dialog box, which gives the user the choice of whether to continue with the action or to abort. This is actually our old friend the system message box. In case you've forgotten, the most useful overload of Show is as follows The two strings are the text and caption body and title of the message box....

Trigonometric functions

All trigonometric functions use radians when an angle is called for. The ratio of degrees to radians is 180 n. sin x , y cos x , y tan x , y The standard trignometric functions. y sin x , y cos x , and y tan x . arcsin x , y arccos x , y arctan x , y The inverse trigonometric functions y sin-1 x , y cos-1 x , y tan-1 x . These return the value of y in radians such that sin y x with y G f cos y x with y 0,7r and tan y x with y f, f , respectively. Returns tan-1 f but takes into account the sign...

Inheritance and Polymorphism

The Circle class builds on the Point class using inheritance. The Circle class adds one additional data attribute radius , and three new methods. It also reimplements a few of Point's methods. Here is the complete class definition def edge_distance_from_origin self return abs self.distance_from_origin - self.radius return self.radius other.radius and super ._eq_ other return Circle 0.radius r , 0.x r , 0.y r .format self Inheritance is achieved simply by listing the class or classes that we...

Times and Dates

The calendar and datetime modules provide functions and classes for date and time handling. However, they are based on an idealized Gregorian calendar, so they are not suitable for dealing with pre-Gregorian dates. Time and date handling is a very complex topic the calendars in use have varied in different places and at different times, a day is not precisely 24 hours, a year is not exactly 365 days, and daylight saving time and time zones vary. The date-time.datetime class but not the...

Command recall

There are many ways to avoid typing within the PyCrust shell. Most of them involve capturing something you have previously entered, modifying it if necessary, and sending it to the Python interpreter. For example, PyCrust maintains a history of all the commands you have entered in the current session. You can recall any previously entered Python commands single-line or multi-line from the command history. Table 4.1 displays a list of keyboard shortcuts that relate to this functionality. Table...

Tridiagonal Coefficient Matrix

Consider the solution of Ax b by Doolittle's decomposition, where A is the n x n tridiagonal matrix As the notation implies, we are storing the nonzero elements of A in the vectors The resulting saving of storage can be significant. For example, a 100 x 100 tridiagonal matrix, containing 10,000 elements, can be stored in only 99 100 99 298 locations, which represents a compression ratio of about 33 1. Let us now apply LU decomposition to the coefficient matrix. We reduce row k by getting rid of...

Linux System Administration Language

Being a sysadmin often means that you get thrown to the wolves. Rules, a predictable schedule, or even choice of an operating system is often out of your control. To be even a marginally effective sysadmin nowadays, you need to know it all, and we mean all the operating systems. From Linux, to Solaris, to OS X, to FreeBSD, it needs to be in your toolbelt. Although only time will tell, it does seem as if the proprietary operating systems, such as AIX and HP-UX, won't last forever, but they still...

Eric4 Ide Applications

Pyqt Gui Prototyping

This book teaches how to write GUI applications using the Python programming language and the Qt application development framework. The only essential prior knowledge is that you can program in some object-oriented programming language, such as C , C , Java, or of course, Python itself. For the rich text chapter, some familiarity with HTML and with regular expressions is assumed, and the databases and threading chapters assume some basic knowledge of those topics. A knowledge of GUI programming...

Introduction to Data Normalization

Data normalization is a way of ensuring that data is maintained in a way that prevents loss of data integrity. If the database structures are not normalized, erroneous code actions, user data-entry mistakes, or system or application failure during the update operation can lead to data corruption. The data corruption I am referring to here is the logical one, whereby the database files are correct but the information stored may be logically incorrect. To continue with the data layout section I...

Divide and Conquer Merge Sort

As discussed above, one technique that often works for developing efficient algorithms is the divide-and-conquer approach. Suppose a friend and I were working together trying to put our deck of cards in order. We could divide the problem up by splitting the deck of cards in half with one of us sorting each of the halves. Then we just need to figure out a way of combining the two sorted stacks. The process of combining two sorted lists into a single sorted result is called merging. If you think...

Example Solution of Differential Equations

An ordinary differential equation ODE , where the unknown is a function u t , can be written in the generic form In addition, an initial condition, u 0 u0, must be associated with this ODE to make the solution of 7.3 unique. The function f reflects an expression with u and or t. Some important examples of ODEs and their corresponding forms of f are given below. 1. Exponential growth of money or populations where a is a given constant expressing the growth rate of u. 2. Logistic growth of a...

Taylor Series

The single most important mathematical tool in computational science is the Taylor series. It is used to derive new methods and also for the analysis of the accuracy of approximations. We will use the series many times in this text. Right here, we just introduce it and present a few applications. A.4.1 Approximating Functions Close to One Point Suppose you know the value of a function f at some point x0, and you are interested in the value of f close to x. More precisely, suppose we know f x0...

Random Walk in Two Space Dimensions

A random walk in two dimensions performs a step either to the north, south, west, or east, each one with probability 1 4. To demonstrate this process, we introduce x and y coordinates of np particles and draw random numbers among 1, 2, 3, or 4 to determine the move. The positions of the particles can easily be visualized as small circles in an xy coordinate system. The algorithm described above is conveniently expressed directly as a complete working program def random_walk_2D np, ns, plot_step...

Boolean Algebra

All decisions in computer programs boil down to appropriate Boolean expressions. The ability to formulate, manipulate and reason with these expressions is an important skill for programmers and computer scientists. Boolean expressions obey certain algebraic laws similar to those that apply to numeric operations. These laws are called Boolean logic or Boolean algebra. Let's look at a few examples. The following table shows some rules of algebra with their correlates in Boolean algebra. a 0 0 a...

Coming Attraction Objects

Have you noticed anything strange about the syntax of the file processing examples To apply an operation to a file, we use dot notation. For example, to read from infile we type infile.read . This is different from the normal function application that we have used before. Afterall, to take the absolute value of a variable x, we type abs x , not x.abs . In Python, a file is an example of an object. Objects combine both data and operations together. An object's operations, called methods, are...

Curation Versus Evolution

As large corpora are published, researchers are increasingly likely to base their investigations on balanced, focused subsets that were derived from corpora produced for entirely different reasons. For instance, the Switchboard database, originally collected for speaker identification research, has since been used as the basis for published studies in speech recognition, word pronunciation, disfluency, syntax, intonation, and discourse structure. The motivations for recycling linguistic corpora...

Command Line Programming

If we need a program to be able to process text that may have been redirected in the console or that may be in files listed on the command line, we can use the fileinput module's fileinput.input function. This function iterates over all the lines redirected from the console if any and over all the lines in the files listed on the command line, as one continuous sequence of lines. The module can report the current filename and line number at any time using fileinput.filename and fileinput.lineno...

Calculator example source code

Python Codes Tkinter

Import Pmw O Python MegaWidgets SLabe1 defines a 2-sided 1abe1 within a Frame. The 1eft hand 1abe1 has b1ue 1etters the right has white 1etters. def _init_ se1f, master, 1eft1, right1 Frame._init_ se1f, master, bg 'gray40' se1f.pack side LEFT, expand YES, fi11 BOTH Labe1 se1f, text 1eft1, fg 'stee1b1ue1', font aria1, 6, bo1d , width 5, bg 'gray40' .pack side LEFT, expand YES, fi11 BOTH Labe1 se1f, text right1, fg 'white', font Maria1, 6, Mbo1d , width 1, bg 'gray40' .pack def _init_ self,...

Software Company Sells A Package That Retails For 99 Python Program

The area of a rectangle is the rectangle's length times its width. Write a program that asks for the length and width of two rectangles. The program should tell the user which rectangle has the greater area, or if the areas are the same. Scientists measure an object's mass in kilograms and its weight in newtons. If you know rhe amount of mass of an object in kilograms, you can calculate its weight in newtons with the following formula Write a program that asks the user to enter an object's...

Canvas rectangle objects

Each rectangle is specified as two points x0, y0 is the top left corner, and x1, y1 is the location of the pixel just outside of the bottom right corner. For example, the rectangle specified by top left corner 100,100 and bottom right corner 102,102 is a square two pixels by two pixels, including pixel 101,101 but not including 102,102 . The outline lies inside the rectangle on its top and left sides, but outside the rectangle on its bottom and right side. The default appearance is a...

Future Value with a Function

Now that you've seen how defining functions can help solve the code duplication problem, let's return to the future value graph. Recall the problem is that bars of the graph are printed at two different places in the program. The code just before the loop looks like this. Draw bar for initial principal bar Rectangle Point 0, 0 , Point 1, principal And the code inside of the loop is as follows. bar Rectangle Point year, 0 , Point year 1, principal Let's try to combine these two into a single...

Common Programming Error

Failure to indent all statements that belong to an if suite or an else suite results in a syntax error. The flowchart of Fig. 3.4 illustrates the flow of control in the if else structure. Once again, note that besides small circles and arrows the symbols in the flowchart are rectangles for actions and diamonds for decisions . We continue to emphasize this action decision model of computing. Imagine again a bin containing empty double-selection structures. The programmer's job is to assemble...

Semaphore and Bounded Semaphore

A semaphore is a synchronization primitive based on a counter that's decremented by each acquire call and incremented by each release call. If the counter ever reaches zero, the acquire method blocks until some other thread calls release . Creates a new semaphore. value is the initial value for the counter. If omitted, the counter is set to a value of 1. A Semaphore instance, s, supports the following methods Acquires the semaphore. If the internal counter is larger than zero on entry, this...

Searching Text

Programming Languages Over Time

There are many ways to examine the context of a text apart from simply reading it. A concordance view shows us every occurrence of a given word, together with some context. Here we look up the word monstrous in Moby Dick by entering text1 followed by a period, then the term concordance, and then placing monstrous in parentheses gt gt gt Building index Displaying 11 of 11 matches ong the former , one was of a most monstrous size . This came towards us , ON OF THE PSALMS . Touching that monstrous...

Python Pros and Cons

Python has more extension modules than the other languages. Many online Python tutorials exist. There are also plenty of English books and reference materials, many sample scripts exist online, and there is a wealth of introductory material. The Python.org Website is a good place to start looking for these because it has sections for beginners, tutorials, guides organized by topic, and lists of links and references. Most folks really enjoy the syntax of the Python language because it appears...

Example Moving Average

Numpy Smooth List

On many occasions, filtering is used to smooth a signal. A simple algorithm is that of a moving average. For every two consecutive points, we calculate the average and use that value instead. The points are overlapping, so a result of using the algorithm on the vector l, 2, 0, 2 would be 1.5, 1, l . But why stop at two samples Moving average can be performed on several points, returning the average of those points. In Python, you could write gt gt gt from pylab import gt N 512 gt gt gt x l-exp...

Ten in a row

Let's do one more probability experiment before we move on. A few pages ago, we talked about flipping a coin and how likely it would be to get a bunch of heads in a row. Why don't we try an experiment to see how often we get 10 heads in a row It won't happen very often, so we're going to have to do a lot of coin flips before we see it. Why don't we try 1,000,000 With a real coin, that would take . . . a long time. If you could do one coin toss every 5 seconds, that would be 12 per minute, or...

Programming Exercises

Write a function named f eet_to_inches that accepts a number of feet as an argument, and returns the number of inches in that many feet. Use the function in a program that prompts the user to enter a number of feet and then displays the number of inches in that many feet. Write a program that gives simple math quizzes. The program should display two random numbers that are to be added, such as 247 129 The program should allow the student to enter the answer. If the...

KU of Decorator

Gzip.GzipFile decorates a file with compress decompress functionality 0 threading.RLock decorates thread.Lock with reentrancy amp ownership functionality 0 codecs classes decorate a file with generic encoding and decoding functionality client code y needs to access an object t 0 however, something interferes w that amp t lives remotely, or in persisted form access restrictions may apply security amp lifetime or performance issues 0 proxy object tt sneaks in the middle 0 tt wraps t, may create...

Write A For Loop To Read The Contents Of Alkaline Metals.txt And Store It In A Nested List With Each Element Of The

Here are some exercises for you to try on your own 1. Assign a list that contains the atomic numbers of the six alkaline earth metals beryllium 4 , magnesium 12 , calcium 20 , strontium 38 , barium 56 , and radium 88 to a variable called alkaline_earth_metals. 2. Which index contains Radium's atomic number Write the answer in two ways, one using a positive index and one using a negative index. 3. Which function tells you how many items there are in alkaline_ earth_metals 4. Write code that...

Your First Python CGI Script Hello Apache

The CGI Common Gateway Interface protocol is a standard way for external programs and application environments to interact with Web servers. While a plain HTML file on the Web is static, a CGI program or script is executed at the time that the request is made from the user, and the content is created on the fly. To see how this works, let's create a simple script in Python and have it executed by the Apache Web server. 1. Create a new file using the IDLE editor or your favorite text editor. 2....

Python Program On Miles Per Gallon Loop

A few lines of code using Boolean operators this way. If Just make sure that your code doesn't get so tricky that 1. Compare and contrast the following pairs of terms. a Definite loop vs. Indefinite loop c Interactive loop vs. Sentinel loop d Sentinel loop vs. End-of-file loop 2. Give a truth table that shows the Boolean value of each of the following Boolean expressions, for every possible combination of input values. Hint including columns for intermediate expressions is helpful. 3. Write a...

Design A Program That Asks The User To Enter A Store S Sales For Each Day Of The Week

Alphabetic Telephone Number Translator Many companies use telephone numbers like 555-GET-FOOD so the number is easier for their customers to remember. On a standard telephone, the alphabetic letters are mapped to numbers in the following fashion A, B, and C 2 D, E, and F 3 G, H, and I 4 J, K, and L 5 M, N, and O 6 P, Q, R, and S 7 T, U, and V 8 W, X, Y, and Z 9 Write a program that asks the user to enter a 10-character telephone number in the format XXX-XXX-XXXX. The application should...

Rolling the dice

Almost everyone has played a game using dice. Whether it's Monopoly, Yahtzee, Trouble, Backgammon, or some other game, rolling dice is one of the most common ways to generate a random event in a game. Dice are very easy to simulate in a program, and Python's random module has a couple of ways to do it. One is the randint function, which picks a random integer. Because the number of spots on the sides of a die are integers 1, 2, 3, 4, 5, and 6 , rolling a single die could be simulated like this...

Polynomial Dict1.py

Make a very simple class. Make a class Simple with one attribute i, one method double, which replaces the value of i by i i, and a constructor that initializes the attribute. Try out the following code for testing the class s2 Simple 'Hello' s2.double s2.double print s2.i s2.i 100 print s2.i Before you run this code, convince yourself what the output of the print statements will be. Name of program file Simple.py. o Exercise 7.3. Extend the class from Ch. 7.2.1. Add an attribute...

Dynamic Programming

Dynamic programming is a general technique for designing algorithms which is widely used in natural language processing. The term programming is used in a different sense to what you might expect, to mean planning or scheduling. Dynamic programming is used when a problem contains overlapping subproblems. Instead of computing solutions to these subproblems repeatedly, we simply store them in a lookup table. In the remainder of this section, we will introduce dynamic programming, but in a rather...

Python Programming Exercises Ask User For 4 Numbers Absolute Value

Show the result of evaluating each expression. Be sure that the value is in the proper form to indicate its type int, long int, or float . If the expression is illegal, explain why. 2. Translate each of the following mathematical expressions into an equivalent Python expression. You may assume that the math library has been imported via import math . 3. Show the list of numbers that would be generated by each of the following range expressions. 4. Show the output that would be generated by...

The Engine and the Game Loop

A number of actions must happen in the engine and game loop, and these actions should correspond to a codeable function. You must have a function to remove any sprites that aren't being used and add any new ones, a function to render the screen and background, a function that keeps track of time and updates the game state, a function that does the blitting, and a function that listens for player keystrokes render_frame. Updates and redraws. engine_init. Sets screen and video. engine_loop. Main...

Nagios PlugIn Architecture

The power of Nagios NMS is in its plug-in architecture. All check commands are external utilities that can be written in any language C, Python, Ruby, Perl and so on. The plug-ins communicate with the Nagios system by means of OS return codes and the standard input output mechanism. In other words, Nagios has a predefined set of return codes that the check scripts must return. The return code dictates what the new service state should be set to. All return codes and the corresponding service...

Predefined Exception Classes

The following exceptions are raised by programs Failed attribute reference or assignment. EOFError End of file. Generated by the built-in functions input and raw_input . It should be noted that most other I O operations such as the read and readline methods of files return an empty string to signal EOF instead of raising an exception. Failed floating-point operation. It should be noted that floating-point exception-handling is a tricky problem and only that this exception only gets raised if...

Programming an Encoder

Let's return to the note-passing example. Using the Python ord and chr functions, we can write some simple programs that automate the process of turning messages into strings of numbers and back again. The algorithm for encoding the message is simple. print the letter number of the character Getting the message from the user is easy, a raw_input will take care of that for us. message raw_input Please enter the message to encode Implementing the loop requires a bit more effort. We need to do...

While Repetition Structure

A repetition structure allows the programmer to specify that a program should repeat an action while some condition remains true. The pseudocode statement While there are more items on my shopping list Purchase next item and cross it off my list 26, Nov 16 2001, 11 44 11 MSC 32 bit Intel on copyright, credits or license for more informa- describes the repetition that occurs during a shopping trip. The condition, there are more items on my shopping list is either true or false. If it is true,...

Defensive Programming

In order to avoid some of the pain of debugging, it helps to adopt some defensive programming habits. Instead of writing a 20-line program and then testing it, build the program bottom-up out of small pieces that are known to work. Each time you combine these pieces to make a larger unit, test it carefully to see that it works as expected. Consider adding assert statements to your code, specifying properties of a variable, e.g., assert isinstance text, list . If the value of the text variable...

Drawing on a canvas

Python Tkinter Canvas Example

We have already encountered several examples of objects drawn on canvases. However, these objects were drawn to represent physical objects on front panels and to create images pro-grammatically. Now we need to allow the user to create drawn objects on the canvas. Almost all drawing operations define a bounding box which encloses the object. The bounding box is expressed as a pair of x y coordinates at the top-left and bottom-right corners. Lines are special cases they have a start and end...

Functions that Return Values

You have seen that parameter passing provides a mechanism for initializing the variables in a function. In a way, parameters act as inputs to a function. We can call a function many times and get different results by changing the input parameters. Sometimes we also want to get information back out of a function. This is accomplished by having functions return a value to the caller. You have already seen numerous examples of this type of function. For example, consider this call to the sqrt...

How can I get those neat updown arrow buttons

A spinner is a combination text control and pair of arrow buttons that adjust a numeric value, and is a great alternative to a slider when you have minimal screen space. Figure 7.8 displays a wxPython spinner control. In wxPython, the wx.SpinCtrl class manages both the spinner buttons and the associated text display. In the next section, we'll create a spinner. Figure 7.8 A spinner control in wxPython Figure 7.8 A spinner control in wxPython Use wx.SpinCtrl to change the value either by...

Virtual Pet Programming

We're going to make a very simplified Virtual Pet program, which, as we indicated, is a kind of simulation. You can buy virtual pet toys like a keychain with a small screen and download virtual pet software. There are also web sites like Neopets and Webkinz, which are forms of virtual pets. All of these, of course, are simulations as well. They mimic the behavior of a living thing and get hungry, lonely, tired, and so on. To keep them happy and healthy, you have to feed them, play with them, or...

Case Study Roman Numerals

You've most likely seen Roman numerals, even if you didn't recognize them. You may have seen them in copyrights of old movies and television shows Copyright MCMXLVI instead of Copyright 1946 , or on the dedication walls of libraries or universities established MDCCCLXXXVIII instead of established 1888 . You may also have seen them in outlines and bibliographical references. It's a system of representing numbers that really does date back to the ancient Roman empire hence the name . In Roman...

The Word Net Hierarchy

Wordnet Hierarchy

WordNet synsets correspond to abstract concepts, and they don't always have corresponding words in English. These concepts are linked together in a hierarchy. Some concepts are very general, such as Entity, State, Event these are called unique beginners or root synsets. Others, such as gas guzzler and hatchback, are much more specific. A small portion of a concept hierarchy is illustrated in Figure 2-8. Figure 2-8. Fragment of WordNet concept hierarchy Nodes correspond to synsets edges indicate...

Shape functions

Force a sequence of arrays including array scalars to each be at least 1-d. Force a sequence of arrays including array scalars to each be at least 2-d. Dimensions of length 1 are pre-pended to reach a two-dimensional array. Force a sequence of arrays including array .scalars to each be at least 3-d. Dimensions of length 1 are pre-pended to reach a two-dimensional array. Return a new array with the contents of arr shifted rolled by the amount given in the integer argument shift along the axis...

Converting Fahrenheit to Celsius

The code for converting the other way from Fahrenheit to Celsius is very similar. The formula for that conversion is . ,c , It goes in the event handler for the Fahrenheit to Celsius button def on_btnFtoC_mouseClick self, event We need to get the Fahrenheit temperature from the spinner fahr self.components.spinFahr.value This value is already an integer, so we don't have to do any type conversion. Then we apply the formula , , . c . , 0 string and put it in the Celsius text box...

Test Your Knowledge Quiz

What is the output of the following code, and why gt gt gt def func a, b 4, c 5 print a, b, c 2. What is the output of this code, and why gt gt gt def func a, b, c 5 print a, b, c 3. How about this code what is its output, and why gt gt gt def func a, pargs print a, pargs 4. What does this code print, and why gt gt gt def func a, kargs print a, kargs 5. One last time what is the output of this code, and why gt gt gt def func a, b, c 3, d 4 print a, b, c, d gt gt gt func 1, 5,6 6. Name three...

The numberguessing game again

Easygui Integerbox

In chapter 1, we made a simple number-guessing program. Now let's try the same thing, but using EasyGui for the input and output. Listing 6.5 has the code. Listing 6.5 Number-guessing game using EasyGui secret random.randint 1, 99 guess 0 tries 0 easygui.msgbox AHOY I'm the Dread Pirate Roberts, and I have a secret It is a number from 1 to 99. I'll give you 6 tries while guess secret and tries lt 6 guess easygui.integerbox What's yer guess, matey if not guess break if guess lt secret...

Lua Pros and Cons

Lua is probably the fastest of the three languages and usually uses the least amount of runtime memory. Lau has the smallest memory footprint for bundling. The Lau C API is very well documented and has good examples for integrating with C. The documentation has improved but is still a bit sketchy overall. Of the three languages, Lua it is probably the least documented the API being the exception , with the least amount of code comments. This makes for the largest ramp-up time to learn, and...

You Are To Write A Program That Calculates The Amount Of Money A Person Would Earn Over A Period Of Time If His Or Her

Where F is the Fahrenheit temperature and C is the Celsius temperature. Your program must use a loop to display the table. Write a program that calculates the amount of money a person would earn over a period of time if his or her salary is one penny the first day, two pennies the second day, and continues to double each day. The program should ask the user for the number of days. Display a table showing what the salary was for each day, and then show the total pay at the end of the period. The...

Custom Modules

Since modules are just .py files they can be created without formality. In this section we will look at two custom modules. The first module, TextUtil in file TextUtil.py , contains just three functions is_balanced which returns True if the string it is passed has balanced parentheses of various kinds, shorten shown earlier 177 lt , and simplify , a function that can strip spurious whitespace and other characters from a string. In the coverage of this module we will also see how to execute the...

Connect the dots

Pygame Tutorial

If you look really closely, you might notice that the sine wave isn't continuous there are spaces between the points in the middle. That's because, at the steep part of the sine wave, we have to move up or down by 3 pixels when we move one pixel to the right. And because we're drawing individual points, not lines, there's nothing to fill the space in between. Let's try the same thing using a short line to join each plot point. Pygame has a method to draw a single line, but it also has a method...

Propositional Logic

A logical language is designed to make reasoning formally explicit. As a result, it can capture aspects of natural language which determine whether a set of sentences is consistent. As part of this approach, we need to develop logical representations of a sentence 9 that formally capture the truth-conditions of 9. We'll start off with a simple example 8 Klaus chased Evi and Evi ran away . Let's replace the two sub-sentences in 8 by 9 and respectively, and put amp for the logical operator...

Binding widgets to dynamic data

Tkinter provides a simple mechanism to bind a variable to a widget. However, it not possible to use an arbitrary variable. The variable must be subclassed from the Variable class several are predefined and you could define your own, if necessary. Whenever the variable changes, the widget's contents are updated with the new value. Look at this simple example def _init_ self, master None, label '', value 0 self.i Checkbutton master, text label, variable self.var, command self.valueChanged...

Installing on Mac OS X

Mac Pyqt Xcode

To install PyQt on Mac OS X, you must already have the Xcode tools installed. This is because a compiler and build tool are required to install PyQt. Xcode is a very large package, normally supplied on a separate developer's CD provided with the machine it is also available online from http developer.apple. com tools xcode. The following instructions assume that Xcode is already installed. Although Macs are normally supplied with a version of Python preinstalled, it may be an old version, in...

Declarative Programming

List comprehensions and generator expressions are strongly tied to operations found in declarative languages. In fact, the origin of these features is loosely derived from ideas in mathematical set theory. For example, when you write a statement such as x x for x in a if x gt 0 , it's somewhat similar to specifying a set such as x2 x a,x gt 0 . Instead of writing programs that manually iterate over data, you can use these declarative features to structure programs as a series of computations...

Exercise 6.4 Draw A Stack Diagram For The Following Program

Exercise 6.4 Draw a stack diagram for the following program. What does the program print prod a z, z print z, prod return prod def a x, y x x 1 return x y sum x y z pow b sum 2 return pow Exercise 6.5 The Ackermann function, A m,n , is defined3 Write a function named ack that evaluates Ackerman's function. Use your function to evaluate ack 3, 4 , which should be 125. What happens for larger values of m and n Exercise 6.6 A palindrome is a word that is spelled the same backward and forward, like...

Lunar Lander

We'll start with our spacecraft some distance above the moon's surface. The moon's gravity will start to pull it down, and we'll have to use the thrusters to slow its descent and make a soft landing. Here's what the program will look like The small grey bar on the left side is the throttle. You drag it up or down with the mouse to control the thrust of the engines. The fuel gauge tells you how much fuel you have left, and the text gives you information on your velocity, acceleration, height,...

Plotting

Visualization is the final step, displaying data graphically to the audience, portraying an idea, and capturing information efficiently and elegantly. We now turn to two packages that allow easy plotting and graphing. Plotting throughout the book will rely heavily on the matplotlib package, maintained at http matplotlib.sourceforge.net . Matplotlib isa2-D plotting package that interfaces well with NumPy and SciPy. The package is cross-platform and works on Linux, Windows, and Mac OS. Matplotlib...

Playlist Data Parsing

Hand- In the previous section's second subsection we created a handcrafted regex- PLY crafted based parser for .m3u files. In this subsection we will create a parser to do the m3u m u same thing, but this time using the PyParsing module. An extract from a .m3u parser file is shown in Figure 14.6 523 lt , and the BNF is shown in Figure 14.7 557 As we did when reviewing the previous subsection's .pls parser, we will review the .m3u parser in three parts first the creation of the parser, then the...

Exercises

Make a Fahrenheit-Celsius conversion table. Modify the c2f_table_while.py program so that it prints out a table with Fahrenheit degrees 0,10, 20, , 100 in the first column and the corresponding Celsius degrees in the second column. Name of program file c2f_table_while.py. O Write a program that generates all odd numbers from 1 to n. Set n in the beginning of the program and use a while loop to compute the numbers. Make sure that if n is an even number, the largest generated odd...

Word frequency analysis

As usual, you should at least attempt the following exercises before you read my solutions. Exercise 13.1 Write a program that reads a file, breaks each line into words, strips whitespace and punctuation from the words, and converts them to lowercase. Hint The string module provides strings named whitespace, which contains space, tab, newline, etc., and punctuation which contains the punctuation characters. Let's see if we can make Python swear gt gt gt import string gt gt gt print...

Introduction to GUI Programming

In this chapter we begin with brief reviews of three tiny yet useful GUI applications written in PyQt. We will take the opportunity to highlight some of the issues involved in GUI programming, but we will defer most of the details to later chapters. Once we have a feel for PyQt GUI programming, we will discuss PyQt's signals and slots mechanism this is a high-level communication mechanism for responding to user interaction that allows us to ignore irrelevant detail. Although PyQt is used...

Multithreading

Traditionally, applications have a single thread of execution and perform one operation at a time. For GUI programs this can sometimes be a problem for example, if the user invokes a long-running operation, the user interface might freeze up while the operation is taking place. There are a few solutions that can be tried to eliminate this problem. One simple solution, particularly useful in long-running loops, is to call QAp-plication.processEvents . This method gives the event loop the...

Posixpath

Do not import this module directly, import os instead and refer to this module as os.path. e.g. os.path.exists p Returns absolute path for path, taking current working dir in account. Returns the longuest path prefix taken character-by-character that is a prefix of all paths in list or '' if list empty . directory and name parts of path. See also split. True if path is the path of an existing file or directory. See also lexists. Returns a copy of path with expansion done. Returns string that is...

Creating a deck of cards

Another kind of random event that's used a lot in games is drawing a card. It's random because the deck is shuffled, so you don't know what card is coming next. And every time the deck is shuffled, the order is different. With dice and coin tosses, we said that every toss has the same probability, because the coin or die has no memory. But that's not true with cards. As you draw cards from the deck, there are fewer and fewer cards left in most games, anyway . That changes the probability of...

Smoother animation

So far, we have made our ball move once Let's see if we can get it moving in a more realistic way. When animating things on the screen, it's usually good to move them in small steps, so the motion appears smooth. Let's try moving our ball in smaller steps. We're not just going to make the steps smaller we're going to add a loop to move the ball because we want to make many small steps . Starting with listing 16.13, edit the code so it looks like listing 16.14. Listing 16.14 Moving a beach ball...

Transitive Verbs

Our next challenge is to deal with sentences containing transitive verbs, such as 46 . The output semantics that we want to build is exists x. dog x amp chase angus, x . Let's look at how we can use A-abstraction to get this result. A significant constraint on possible solutions is to require that the semantic representation of a dog be independent of whether the NP acts as subject or object of the sentence. In other words, we want to get the formula just shown as our output while sticking to...

Composite pattern

Python Script Nodal Interface

The composite pattern allows complex tree-like structures to be built from simple components. Composite objects are simply container objects, where the content may actually be another composite object. Traditionally, each component in a composite object must be either a leaf node that cannot contain other objects or a composite node. The key is that both composite and leaf nodes can be treated identically. The UML diagram is very simple This simple pattern, however, allows us to create very...

Playing background music

Background music is meant to play in the background while the game is being played. So once you start the background song, Pygame has to get ready to do other things, like moving sprites around or checking the mouse and keyboard for input. It doesn't wait for the song to finish. But what if you want to know when the song ends Maybe you want to start a different song or play another sound like we want to do . How do you know when the music is done Pygame has a way to tell you you can ask the...

Visual Studio Express and ironPython

Microsoft Visual Express Interface

For this example, we use the free version of Visual Studio, Visual Studio Express. Visual Studio Express doesn't have IronPython integration, so we have to find another way to work with it to create our dialog. Depending on which version you download,9 it can generate Visual Basic, C , C , or Visual J . Because they all compile to .NET assemblies and we won't be directly writing code in this example, it doesn't really matter which one you choose. Having generated code in another language can be...

Description of the megawidget

Arc Pygame

This widget will implement a simple gauge which tracks an integer value supplied by a Scale widget, which selects a number from a range. The gauge indicates the setting as a percentage of the range. The completed megawidget will look like the one shown in figure 4.52. The scale widget will be a component of the megawidget since the range may be set by the programmer the size and color of the gauge may similarly be changed, as appropriate for the application, so we make this a component, too. In...

The for Statement

The for loop is a sequence or other iterable iteration that assigns items in iterable to target and runs the first suite for each. The for statement runs the else suite if the loop exits without hitting a break statement. target can be anything that can appear on the left side of an assignment statement e.g., for x, y in tuplelist . Since Python 2.2, this works by first trying to obtain an iterator object I with iter iterable and then calling that object's I._next_ method repeatedly until...

Working with wxPrintout methods

There are a few getter-type methods in wx.Printout that allow you to retrieve information about the current print environment. Table 17.1 lists these information retrieval methods. Table 17.1 Information retrieval methods of wx.Printout Table 17.1 Information retrieval methods of wx.Printout This method returns the device context to be used for drawing the document for the printer or the print preview. Returns a 4-element tuple minPage, maxPage, pageFrom, pageTo . The minPage and maxPage return...

Pyqt Setsortingenabled Qsqlquerymodel

Page size, printer, 400 Page Designer application, 351-368 pageRect QPrinter , 408 paint devices see QImage, QPainter, QPicture, QPixmap, QPrinter, QSvgGenerator, and QWidget paint 461, 486, 489 QGraphicsItem, 366, 368, 374, 377 paintEvent QWidget , 306, 309, 336, 342,480 palette see QPalette palette QApplication, 438, 489 QWidget, 337 parameters, 55, 56 default, 56 keyword, 55, 59-61 passing by value, 57 positional, 55 parent QObject , 433, 504 parent, of widget, 118,119,172,340, 372...

The Module Search Path

When loading modules, the interpreter searches the list of directories in sys.path.The first entry in sys.path is typically an empty string '', which refers to the current working directory. Other entries in sys.path may consist of directory names, .zip archive files, and .egg files.The order in which entries are listed in sys.path determines the search order used when modules are loaded. To add new entries to the search path, simply add them to this list. Although the path usually contains...

List Comprehensions

List Python

A list comprehension provides a compact way of mapping a list into another list by applying a function to each of the elements of the list. gt gt gt elem 2 for elem in a_list gt gt gt a_list elem 2 for elem in a_list 1. To make sense of this, look at it from right to left. a_list is the list you're mapping. The Python interpreter loops through a_list one element at a time, temporarily assigning the value of each element to the variable elem. Python then applies the function elem 2 and appends...

Speed drawing

In general, creating canvas objects is relatively efficient and rarely causes a performance problem. However, for very complex drawings, you may notice a delay in drawing the canvas. This is particularly noticeable when the display contains a large number of objects or when they contain complex line segments. One way of improving drawing performance is to draw the canvas as an image. The Python Imaging Library, which was introduced briefly in chapter 5 on page 89, has the facility to draw...

Implementing COM Objects in Python

Script Form Edit Delphi

In order to implement COM objects in the Python version of Windows, you need a set of extensions developed by Mark Hammond and Greg Stein. Part of the win32com package, these extensions enable you to do everything that is COM-related, including writing COM clients and COM servers. The following link takes you to the download page of these extensions All the Win32 extensions including the COM extensions are part of the win32all installation package. This package also installs the PythonWin IDE...

PopUp Alert in Lines

Our first GUI application is a bit odd. First, it must be run from the console, and second it has no decorations no title bar, no system menu, no X close button. Figure 4.1 shows the whole thing. Figure 4.1 The Alert program To get the output displayed, we could enter a command line like this C gt cd c pyqt chap04 C pyqt chap04 gt alert.pyw 12 15 Wake Up When run, the program executes invisibly in the background, simply marking time until the specified time is reached. At that point, it pops up...

How do I make a nonrectangular frame

Wxpython Demo

In most applications, frames are rectangles because rectangles have a nice regular shape and are relatively simple for an application to draw and maintain. Sometimes, though, you need to break out of the straight line straitjacket. In wxPython, you can give a frame an arbitrary shape. If an alternate shape is defined, the parts of the frame that are outside the shape are not drawn, and do not respond to mouse events as far as the user is concerned, they are not part of the frame. Figure 8.9...

Introducing httpl i b

Before you can use httplib2, you'll need to install it. Visit code.google.com p httplib2 and download the latest version. httplib2 is available for Python 2.x and Python 3.x make sure you get the Python 3 version, named something like httplib2-python3-0.5.0.zip. Unzip the archive, open a terminal window, and go to the newly created httplib2 directory. On Windows, open the Start menu, select Run , type cmd.exe and press ENTER. c Users pilgrim Downloads gt dir Volume in drive C has no label....

Default Exception Handler

Suppose we write the following function gt gt gt def fetcher obj, index return obj index There's not much to this function it simply indexes an object on a passed-in index. In normal operation, it returns the result of a legal index gt gt gt x 'spam' gt gt gt fetcher x, 3 Like x 3 However, if we ask this function to index off the end of the string, an exception will be triggered when the function tries to run obj index . Python detects out-of-bounds indexing for sequences and reports it by...

Advanced Class Topics

This chapter concludes our look at OOP in Python by presenting a few more advanced class-related topics we will survey subclassing built-in types, new-style class changes and extensions, static and class methods, function decorators, and more. As we've seen, Python's OOP model is, at its core, very simple, and some of the topics presented in this chapter are so advanced and optional that you may not encounter them very often in your Python applications-programming career. In the interest of...

Using the Clipboard

PyQt provides clipboard support for text in QTextEdit, QLineEdit, QTableWidget, and the other widgets where textual data can be edited. PyQt's clipboard and drag-and-drop systems use data in MIME Multipurpose Internet Mail Extensions format, a format that can be used to store any arbitrary data. Occasionally, it is convenient to pass data to the clipboard or retrieve data from the clipboard directly in code. PyQt makes this easy. The QApplication class provides a static method that returns a...

Database Programming

For traditional database demands, there are Python interfaces to all commonly used relational database systems Sybase, Oracle, Informix, ODBC, MySQL, PostgreSQL, SQLite, and more. The Python world has also defined a portable database API for accessing SQL database systems from Python scripts, which looks the same on a variety of underlying database systems. For instance, because the vendor interfaces implement the portable API, a script written to work with the free MySQL system will work...

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