Info Tch
information stored in the cookie for the system. The modification form is really exactly the same as the add book record form, except that it comes pre-populated. You may or may not use the same script behind the scenes to work on the forms, but the design is the same. The purpose of the user interface design segment of the project plan is to discover what elements you need and what elements can be combined together. In addition, by figuring out what you are going to need to do, you can design...
Info Cge
Unlike many things in the programming world, a zero when running a program indicates a successful status, meaning the file was copied. We talked about the files and directories portion of the os module back in Chapter 6, so there is no real reason to rehash it here. Instead, you should spend your time looking through the various components of the modules, to see what you will need when you are writing your own applications in Python. By the way, the win32api modules are all available free of...
File Input
Not all input into an application is from the user on the command line. Quite often, it is necessary to read data from an existing data source, such as a file. Other forms of file input are databases, but we will talk about those later in the book. For now, let's look at the basic file functionality provided with Python and its libraries. The first thing you need to understand is that a file object is a part of the basic Python library. There are no imports necessary to work with files or their...
HTML Elements
Just to illustrate how all of the HTML elements map to their Python equivalents and how you can check to see what you are getting, let's write a very simple program that shows off the various types of HTML elements, such as radio buttons, check boxes, and so forth. Your input form is going to look like the one shown in Figure 13.8, which presents a very simple order form for pizzas. The HTML for this input form looks like this lt TITLE gt Choose your Pizza lt TITLE gt lt FORM lt First, the...
File Output
We've already looked at the methods for reading lines from a file. The next thing to examine is how to write data to a file. For this exercise, it makes sense to work with a real-world example. Let's imagine that we need to be able to log information to a file while our program is running. Now, later on in the book, we would probably use a function that could be used anywhere. However, for now, we will just use interactive statements to accomplish the task. The process of writing to a file is...
Info Sas
As you look at the rather simple code involved in the script, you should notice a few things. First, the code imports two new modules that you haven't really worked with before. The os module contains operating system specific functionality, while the cgi module imports functionality directly related to the CGI processing. We aren't actually using either of these in this script, but you should use them as a matter of course when you are working with Web-related coding. The script uses the print...
Info Rvf
In order to accomplish this, you will first need an input form. This form, which is created in simple HTML, will then call your script. 1. Create a new file using your favorite text editor. In this case, I've chosen to use the Windows Notepad application, which is conveniently available in all versions of Windows. 2. Place the following code into the new file lt Define a form for inputting values for name and address gt lt form lt p gt Enter your first name lt p gt lt input type text name...
Use the compiler to check syntax and convert source into binary format
The purpose of a compiler is to do two things. First, it runs through the tokens in your source code, comparing them to the rules that the language requires. Again, as an example, consider a Pascal assignment statement. The language requires that the statement look something like this In this statement, there are four pieces Q a This is the name of a variable in the program, or a memory address if you prefer. Q -In Pascal, the statement means assign a value to. It takes the variable on the...
Complex Math
If you work in engineering, or electronics, you probably know all about complex math. When we say complex, we are referring here to the combination of real and imaginary numbers. Of course, if you are like me, you think of imaginary numbers as something you find in your checkbook. No, these numbers are really a different form of mathematics. The idea behind complex math is that you have a real portion and an imaginary portion, and these two portions make up a complex number that can be used for...
Understanding Bytecodes
As mentioned previously, Python uses bytecodes to actually do the work of processing the source code. The bytecode idea is not new, as there are quite a number of languages that use something similar. The idea is that a statement is broken down into a code, indicating what it is going to do, and then a series of arguments to that code. For example, you might have something like this The code for print might be 0x01 it doesn't really matter what the value is . The argument to the print statement...
Using the with Clause for Files
One of the most common problems with using exceptions is cleaning up after yourself when something really bad happens. The most common problem is that files are not closed and flushed to disk when you encounter an error in processing them. For this purpose, Python provides a special form of error handling, which is the with clause. The with clause allows you to free up any form of object in a specific block if an error occurs. The basic format of the with clause is as follows Where var is...
Info Hdb
Q Adding a new book record to the system Q Modifying an existing book record in the system Q Deleting an existing book record from the system Q Adding a user review of a book in the system Q Viewing book records in the system Q Viewing book reviews in the system Certainly, there are considerably more flows that you might want in a production environment, but this will easily do for now. Note that not all of these flows require their own individual screens or scripts some can be combined into a...
Cohesion
Cohesion is defined as the way in which the lines of a module work together to accomplish a task. In object-oriented programming, cohesion is primarily identifying overlap between different methods and redundant attributes. We really won't be talking about cohesion at all in this book. Instead, please refer to a really good object-oriented programming and design book such as ones in this series to get a better understanding of concepts like this. For our purposes, we will simply say that...
In Conclusion Ael
In this chapter, we have learned quite a bit about working with Web servers, dynamically generating HTML and HTML forms, working with databases and linking tables, and passing data around between Python scripts. This chapter is not a replacement for a more complete book on SQL or HTML. Instead, it is intended to show you how to work with these concepts within the Python environment. Ifyou plan to work extensively in the Web or database world, I strongly suggest that you find reference works on...
Spanning Multiple Lines
It is quite often useful to have a single string that spans multiple lines. Whether you are out-putting some help text, or just have a quotation that turns out to be too long for a single line of text, Python provides methods for entering multiple lines of text into a single variable. The easiest way to do this is simply to continue a line to the next line by using the line continuation character gt gt gt aQuote This is a really really really long line that needs to be continued to the next...
Rethrowing Exceptions
The final topic of discussion with respect to exceptions and exception handling is how to rethrow an exception. Suppose, for example, that you want to handle certain errors in a function, but you want to allow the calling function to handle them as well. Examples might include simply logging the error and then allowing the calling program to handle it, or perhaps doing some cleanup before letting the caller know things went wrong. In either case, Python permits you to pass an exception back up...
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....
Triple Quotes
The third method for continuing lines in Python was designed for use in printing out things like Help texts or copyright statements. Certainly, you have seen blocks like this Help - use this command for getting help. Our interpreter understands the following commands Print Quit Store This syntax is so popular, in fact, that Python provides a special way to enter it, the triple quote. The triple quote, which is literally three quotation marks in a row, treats everything within the block defined...
Concatenating Strings
After storing and printing, the most utilized function of strings is concatenating, or combining, them into longer strings. For example, I might have an output line that was going to print something based on certain criteria. The beginning of the output might always be the same, say, The answer is where the end of the string would vary, depending on exactly what that answer was. Python provides the string concatentation operation, ' ', for working with strings. Much as the plus operator adds...