delphi How to correctly write Try .Finally..Except statements?

If its an all-or-nothing fail, then the first format makes sense. If you want to be able to process/return all the non-failing elements, you need to use the second form. Those would be my basic criteria for choosing between the methods. Personally, if it is all-or-nothing, I wouldn’t use the second form. I agree with all the performance and readability posts.

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Its more like runtime debugging than normal runtime error detection. Assertions can be disabled if you use the -O flag or run from .pyo files instead of .pyc files, so they should not be part of regular error detection. Because this question may lead to opinionated discussion, debate, and answers, it has been closed. You may edit the question if you feel you can improve it so that it requires answers that include facts and citations or a detailed explanation of the proposed solution. If edited, the question will be reviewed and might be reopened.

Once you enter the try/finally block, the code in the finally section is guaranteed to run, no matter what happens between try and finally. Basically I sometimes have some procedures that may be similar to the first sample I posted, and if I get an error the cursor is stuck as an Hour Glass. Adding the Exception handlers help, but it seems a dirty way of doing it – its basically ignoring the Finally block, not to mention ugly code with copy-paste from the Finally to Exception parts. __try / __except is for catching SEH (windows generated errors) not for catching general exceptions.

If you tried to do work in catch block it might throw another exception – I guess that’s where the else block comes handy. Basically, it comes down to doing different exception handling in different parts of the algorithm. This is a great way of accidentally hiding severe bugs in your code. I typo-ed cleanup there, but the AttributeError that would let me know is being swallowed. Try / catch is what the C++ standard specifies for handling general C++ exceptions. On Windows, exceptions are supported at the operating system level.

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But if the exception can be predicted, you should always choose validation beforehand over an exception. However, not everything can be predicted, so this code pattern has its place. An else block can often exist to complement functionality that occurs in every except block. The ‘else’ block of a try-except clause exists for code that runs when (and only when) the tried operation succeeds.

The guideline to follow is that you should use finally rather than except for protecting resources. As you have observed, if you attempt to do it with except then you are forced to write the finalising code twice. Of course, I’m describing this as a pattern that may turn up in your own code someday. In this specific case, you just set inconsistency_type to 0 before the try block anyway. Here you have the variable something defined if no error is thrown.

Advanced version, when json object is expected to be returned

2/ Raise can also be used to re-raise the current error to pass it up the stack to see chicken road if something else can handle it. In my opinion, this would be the most Pythonic way to handle it, although and because it makes your question moot. Note that this defines __getattr__() instead of __getattribute__() , because doing so means it only has to deal with the “special” attributes being kept in the internal dictionary.

The other answers miss that last part.

However, there are cases where it really does matter. A couple other people mentioned this, but it might be easier to see with examples. If the Obj creates other things inside it’s constructor, it may work half-way and fail with an exception inside the .create(); but still be a created Obj. So I make sure that the Obj is always destroyed if it’s been assigned…

If it can prove that there’s no throw statement inside the scope block that controls the object’s lifetime then it skips the registration code. This is not compatible with asynchronous SEH exceptions, you should use the /EHa compile option to suppress this optimization if you intend to catch SEH exceptions. The use of the else clause is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the try … The use of the else clause is better than adding additional code tothe try clause because it avoids accidentally catching an exceptionthat wasn’t raised by the code being protected by the try … As long as you are aware of what you need to accomplish in the loop you could put the try catch outside the loop. But it is important to understand that the loop will then end as soon as the exception occurs and that may not always be what you want.

If you don’t want to chain (a huge number of) try-except clauses, you may try your codes in a loop and break upon 1st success. If production quality code raises an exception, then figure out what you did wrong. If it raises an AssertionError, you’ve got a bigger problem.

• Because if you get an error, or not, you only want to release your database connection (or pick your favorite type of other resource…) once.
• The intended use is to have a context for more code to run if there were no exceptions where it was expected to be handled.
• Think about what would be interesting to you in the debugger at this point in the program.
• I like to avoid raising a new exception while handling an old one.
• It’s a matter of preventing exceptions as much as you can.
• That will raise an HTTPError, if the response was an http error.

Connect and share knowledge within a single location that is structured and easy to search. I’m using except ExplicitException here because it is never a good practice to blindly ignore all exceptions. You’ll be ignoring MemoryError, KeyboardInterrupt and SystemExit as well otherwise, which you normally do not want to ignore or intercept without some kind of re-raise or conscious reason for handling those. Try is used to execute code that might raise an Exception that you’re expecting.

• Instead of stopping the program, you can “catch” the exception and deal with it in your code.
• Here you have the variable something defined if no error is thrown.
• In Python it is easier to ask for forgiveness than permission.

All exceptions that Requests explicitly raises inherit from requests.exceptions.RequestException. If a request times out, a Timeout exception is raised. Maybe it would be better to throw an IllegalArgumentException in the error case instead if returning null. You can keep processing (if you want) or you can throw a helpful exception that tells the client the value of myString and the index of the array containing the bad value.

Likewise the inner try/finally ensures that Obj is destroyed in case of any exceptions being raised during its lifetime. Looking at Python reference it seems that else is executed after try when there’s no exception.The optional else clause is executed if and when control flows off the end of the try clause. 2 Exceptions in the else clause are not handled by the preceding except clauses.

Exceptions are meant to handle errors that might occur in code or events you have no control over. For situations where a function continues after exception-handled code, you can avoid nesting a try/except fallback sequence without needing a helper function to return from by using a dummy loop. If you want to break the loop and examine the Exception whenever thrown, use try…catch out of the loop. This will break the loop and execute statements after catch (if any). If you want to catch Exception for each iteration, or check at what iteration Exception is thrown and catch every Exceptions in an iteration, place try…catch inside the loop. This will not break the loop if Exception occurs and you can catch every Exception in each iteration throughout the loop.

However, since you have to declare a variable for every resource, the advantage of this is debatable. Find centralized, trusted content and collaborate around the technologies you use most.

Where as try, raise and except makeup exception handling which is the preferred way in python to handle and propagate errors. The ones that can be generated by the operating system are listed in the ntstatus.h SDK header file. In addition, you might interop with code that uses SEH to implement their own exception handling, they will use their own exception code. Like .NET, managed exceptions use the 0xe0434f4d (“com”) exception code.