Simple .NET/ASP.NET PDF document editor web control SDK

>>> def handle_exception(): ... try: ... faulty() ... except: ... print 'Exception handled' ... >>> ignore_exception() Traceback (most recent call last): File '<stdin>', line 1, in File '<stdin>', line 2, in ignore_exception File '<stdin>', line 2, in faulty Exception: Something is wrong >>> handle_exception() Exception handled As you can see, the exception raised in faulty propagates through faulty and ignore_exception, and finally causes a stack trace. Similarly, it propagates through to handle_exception, but there it is handled with a try/except statement.

winforms pdf 417 reader, winforms qr code reader, winforms upc-a reader, winforms data matrix reader, winforms gs1 128, winforms ean 13 reader, c# remove text from pdf, pdfsharp replace text c#, winforms code 39 reader, c# remove text from pdf,

In 2 we ran through a multitude of concepts, including variables. Variables are placeholders or references for objects, including numbers, text, or any objects you ve chosen to create. For example:

Here you assign the numeric value of 10 to a variable called x. You can name variables however you like, with only a few limitations. Variable names must be a single unit (no spaces!); must start with either a letter or an underscore; must contain only letters, numbers, or underscores; and are case sensitive. Table 3-1 demonstrates variable names that are valid and invalid.

C-25

Valid Valid Valid Invalid (starts with a digit) Valid Invalid (not a single word) Invalid (contains invalid characters: ', @, and !) Invalid (looks like subtraction)

Variables are important because they allow you to write and use programs that work upon varying data. For example, consider a small program that has the sole job of subtracting two numbers:

Exception handling isn t very complicated. If you know that some part of your code may cause a certain kind of exception, and you don t simply want your program to terminate with a stack trace if and when that happens, then you add the necessary try/except or try/finally statements to deal with it, as needed. Sometimes, you can accomplish the same thing with conditional statements as you can with exception handling, but the conditional statements will probably end up being less natural and less readable. On the other hand, some things that might seem like natural applications of if/else may in fact be implemented much better with try/except. Let s take a look at a couple of examples. Let s say you have a dictionary and you want to print the value stored under a specific key if it is there. If it isn t there, you don t want to do anything. The code might be something like this: def describePerson(person): print 'Description of', person['name'] print 'Age:', person['age'] if 'occupation' in person: print 'Occupation:', person['occupation'] If you supply this function with a dictionary containing the name Throatwobbler Mangrove and the age 42 (but no occupation), you get the following output: Description of Throatwobbler Mangrove Age: 42

C-25 C-27

If the code was written simply as puts 100 - 10, you d get the same result, but it s not as flexible. Using variables, you can get the values for x and y from the user, a file, or some other source. The only logic is the subtraction. As variables are placeholders for values and data, they can also be assigned the results of an expression (such as x = 2 - 1) and be used in expressions themselves (such as x - y + 2). Here s a more complex example:

Step through the example line by line. First you set x to equal 50. You then set y to the value of x * 100 (50 * 100 or 5000). Next you add y to x before printing the result, 5050, to the screen. It makes sense, but the third line isn t obvious at first. Adding y to x looks more logical if you say x = x + y rather than x += y. This is another Ruby shortcut. Because the act of a variable performing an operation upon itself is so common in programming, you can shorten x = x + y to x += y. The same works for other operations too, such as multiplication and division, with x *= y and x /= y being valid too. A common way to increase a variable s value by 1 is x += 1, which is shorthand for x = x + 1.

However, it s best to learn how to develop Rails applications in full first, produce a few throwaway applications, and then retreat to look at testing once the framework is entirely familiar to you.

C-29