Exception Vs Assertion

assert vs exception python
c++ assert
c# assertions vs exceptions
which of the following is not a reason exceptions are better than assert statements?
assert python
c++ exceptions
c++ exception handling best practices
c assert with message

What is the difference between Java exception handling and using assert conditions?

It's known that Assert is of two types. But when should we use assert keyword?

Use assertions for internal logic checks within your code, and normal exceptions for error conditions outside your immediate code's control.

Don't forget that assertions can be turned on and off - if you care about things like argument validation, that should be explicit using exceptions. (You could, however, choose to perform argument validation on private methods using assertions, on the grounds that a violation at that point is due to an internal bug rather than an external error.)

Alternatively it's entire reasonable (IMO) to use exceptions for everything. I personally don't use assertions much at all, but it's a matter of personal preference to some extent. (There can certainly be objective arguments for and against assertions, but it's not sufficiently clear cut to remove preference altogether.)

Exception vs Assert?, My rule of thumb: Exceptions are used for run-time error conditions (IO errors, out of memory, can't get a database connection, etc.). Assertions  An exception may be caught and recovered from. The concept we're interested in here is the Zen Nature of the condition we're testing. Exceptions and Errors in Java are merely implementation techniques. An assertion may well be implemented with exceptions, but its Zen Nature is not to be caught.

Assertations vs. Exceptions, A perfectly adaquate (if ugly) implementation of assertions would be: if (​ASSERTIONS_ENABLED && !condition()) throw new AssertionError("Bad  An exception is similar to an assertion but the meaning is different. An exception is an unexpected execution event that disrupts the normal flow of the program. Exceptions are used to signal an error condition where a corrective action can be taken (ex. file not found). Exceptions can be caught and recovered from as opposed to assertions.

Exception is a mechanism of checking if the implementation is executing without any expected or unexpected errors or not. So, we see that exceptions are basically used for handling even the unforseen conditions during the execution of an application in a better way and hence using exceptions effectively results into a robust application.

Assertions should never be a part of the implementation of some functionality of the application. They should only be used to verify the assumptions - just to be sure that whatever we assumed while desinging the solution is actually valid in practical as well.

reference: http://geekexplains.blogspot.com/2008/06/asserions-in-java-assertions-vs.html

When to use assertions and when to use exceptions?, Assertions should only be used to verify conditions that should be logically impossible to be false (read: sanity checks). These conditions should only be based  Exceptions are for stuff that doesn't normally happen, but might. Missing files, network outages, perhaps invalid data. Stuff your code can't control. Assertions are for stuff that, if your code is working properly, never happens. They're meant as a double-check while debugging.

Assertions are very similar to exceptions, in fact just like exceptions they will flag a problem, but unlike exceptions - they won’t suggest any alternative execution path, but will simply fail. Why use assertions, if you can do the same thing, plus more with exceptions ?

Use them when the problems should not be fixed, and actually SHOULD NEVER HAPPEN IN THE FIRST PLACE. This sounds weird at first: don’t we want to safeguard our code from ALL potential problems ? Usually yes. But there is a case where we don’t. This case is called: "Design by contract".

Let say you are writing an application for a bank. As a developer you can not possibly support all possible financial conditions. So before starting to code, you get a spec from the bank which gives you the valid ranges that this application should support. So your application is designed by a contract (by the spec from the bank). This contract will define the fundamental principles that should always be true in order for your application to work. These fundamental principles are called "invariants" (because they can’t change). Design by contract simplifies your life as a developer - you are only responsible to support the scope of work defined in the contract. Its important to check the values of these invariants in your code, but you shouldn’t check them as if they are exceptions and try to work around them. If they are wrong - you must fail because the inputs have not fulfilled their contractual obligations.

The interesting thing is: if you don’t put an assertion into the critical place and invariants become invalid - your code will fail anyway. You just won’t know why. So to summarize - assertions are used for verifying the invariants. They go hand-in-hand with the "design by contract" principle. Use them to debug a problem, thats why they are turned off in production.

Another use case: if you are relying on an external library that you don’t completely trust - you may want to use assert statements when calling it.

Some also use assertions as a quick and dirty substitute for an exception (since its so easy to do), but conceptually that is not the proper thing to do.

Modern C++ best practices for exceptions and error handling , about the difference of Python's assert keyword vs. raising “normal” exceptions. For quite a long time, I was uncertain when to use assert , too. Exceptions vs. assertions Exceptions and asserts are two distinct mechanisms for detecting run-time errors in a program. Use asserts to test for conditions during development that should never be true if all your code is correct.

Example of a good use of Assert:

assert flibbles.count() < 1000000; // too many flibbles indicate something is awry
log.warning("flibble count reached " + flibbles.count()); // log in production as early warning

I personally think that Assert should only be used when you know something is outside desirable limits, but you can be sure it's reasonably safe to continue. In all other circumstances (feel free point out circumstances I haven't thought of) use exceptions to fail hard and fast.

The key tradeoff for me is whether you want to bring down a live/production system with an Exception to avoid corruption and make troubleshooting easier, or whether you have encountered a situation that should never be allowed to continue unnoticed in test/debug versions but could be allowed to continue in production (logging a warning of course).

cf. http://c2.com/cgi/wiki?FailFast see also my c# copy of this answer: Debug.Assert vs. Specific Thrown Exceptions

Assertions and Exceptions – Stefan Scherfke, Throwing exceptions instead of wrapping simple pre/post-conditions into a simple assertion macro is an hint of the fact that you're coding badly. Tests whether the code specified by delegate action throws exact given exception of type T (and not of derived type) and throws. if code does not throws exception or throws exception of type other than T. Tests whether the code specified by delegate action throws exact given exception of type T (and not of derived type) and throws.

Asserts vs Exceptions, Exceptions: what, how in Java. – How to throw, catch, and declare exceptions. – Subtyping of exceptions. – Checked vs. unchecked exceptions. • Exceptions:  When an exception occurs, the debugger writes an exception message to the Output window. It may break execution in the following cases when: An exception is thrown that isn't handled. The debugger is configured to break execution before any handler is invoked. You have set Just My Code,

[PDF] Lecture 15 Assertions & Exceptions, 1.5 Checked vs. Unchecked Exceptions. As illustrated, the subclasses of Error and RuntimeException are known as unchecked exceptions. These exceptions  Java Assertion - Assertion is a statement in java. It can be used to test your assumptions about the program. Let's see its advantage and example of assertion in java.

Exception Handling & Assertion in Java, try/except blocks let you catch and we can manage exception or add custom exceptions. Exceptions can be triggered by raise , assert , and a large number of​  The big difference between using assertions vs using exceptions is that assertions can be disabled globally in most programming languages. Usually this is done to speed up release builds of a program. Regular exceptions will continue to function as normal. The fact that assertions can be disabled is a deliberate design decision.

Comments
  • I cannot believe my eyes: this question was actually edited by a 166k user and it still looks like this!
  • Yeah, pretty bad. I cleaned it up some more. Not sure what JavaResp means by "two type" so left that in there. My best guess is pre-condition vs post-condition as per deitel.com/articles/java_tutorials/20060106/Assertions.html
  • "Some more" meaning "entire revamp" in this case.
  • It's worth noting that some languages actually implement assertions using exceptions. In such languages your statement that "it's reasonable to use exceptions for everything" is so true it's redundant. :)
  • As specified by dasblinkenlight : "Unchecked exceptions are designed to detect programming errors of the users of your library, while assertions are designed to detect errors in your own logic. These are separate issues that should not be mixed."
  • assetion in run time?
  • and exception in executing timetime?
  • @teranteshara: Yes, they're only checked at execution time (unless you have a special extra compile-time plugin). But they're only checked if they're enabled. See docs.oracle.com/cd/E19683-01/806-7930/6jgp65ikq/index.html
  • The "turning off" is because assertions can be used to verify the result of an optimized algorithm by comparing its implementation against a well-known, but slow, algorithm. So, in development it is ok to invoke that O(n3) method to assert that the O(log N) algorithm works as intented... But is something that you do not want in production.
  • Assertions are much, much stronger statements than that. They're meant to document (and when running in debug, to verify) your assumptions and/or guarantees about what will always be true at a particular point in the code. Assertion failures should never, ever happen -- if they do, it means that (a) your assumptions were wrong, and (b) any code from then on can't be trusted to do the right thing (cause somewhere along the line, it's already done the wrong thing, and now it's operating "out of bounds").
  • If you know that something should never happen then why would you let it pass unchecked in production code where assertions are turned off? Surely you would use an exception to make sure the broken assumption is caught. I know I'm going against the received wisdom here, but I'm interested to see what compelling arguments I can unearth by being contrarian. Thanks for your comment!
  • Exceptions are for stuff that doesn't normally happen, but might. Missing files, network outages, perhaps invalid data. Stuff your code can't control. Assertions are for stuff that, if your code is working properly, never happens. They're meant as a double-check while debugging. In production, your code should already be sure enough of the result that it doesn't even have to check anymore.
  • Doesn't that rather presume that the code (and code around it) never changes? Code evolves in most environments I've seen, touched by many developers, nothing is certain.
  • It presumes that developers won't be putting stuff into production without running it in debug mode first (and causing the code to fail whatever assertions it's invalidated). If the change causes an assertion failure, either your code is wrong (by making unwarranted assumptions) or theirs is (by breaking explicitly stated invariants), and that wrongness is severe enough that it should be fixed before ever considering putting the code in production.