I want to know what is the usefulness of tdie comparing to Java exceptions in talend knowing that when an exception occur tdie exit the job and is passing the error to tlogcatcher .The same thing can be done by java exceptions (they also can be received by tlogcatcher and they exit the job ).
So why java exceptions are not enough for logging so we use tdie?/what is the limits of java exceptions.
I don't use tDie after a component exception (like Component-->oncomponenterror-->tDie . As you stated, the java exception is caught : if you put a tDie, you'll only have 2 lines logged instead of just one.
I use tDie to put an end to a job if a condition is not met : for example , I can test the number of lines inserted in a DB, if it is 0 , I call tDie to end the job (with tDBOutput--if-->tDie , with a test on number of lines inserted inside the if condition).
This is more like a functional error than a technical one that I want to catch in this case.
Related
I'm making a custom plugin to query a database for user info to aide customer support. My backend is slack.
Everytime I start the bot command I'm greeted with:
Computer says nooo. See logs for details:
catching classes that do not inherit from BaseException is not allowed
I'm not sure if this is warning me that I'm attempting to catch an exception that isn't a BaseClass in my code or if an unknown exception was raised and caught elsewhere outside of my plugin.
To debug I tried:
try:
do_the_thing()
except (TypeError, ValueError) as e:
return('Something went wrong.')
I also tried:
try:
do_the_thing()
except Exception as e:
return('Something went wrong.')
And I still get the errbot admonition. Note that the command still runs and does the right thing where there is no exception raised by do_the_thing().
It means that:
Somewhere in your code you have an except ... statement where the exception ... (or one of the exceptions in the sequence ...) is not a subclass of BaseException, and
An exception is being thrown that is caught by that except ... statement.
The TypeError can be raised only when an exception is actually thrown because the names you give to except ... must be evaluated for their current values at that time; just because TypeError referenced a particular class at one point in the program's execution doesn't mean it won't be changed later to reference another object (though that would be admittedly perverse).
The Python interpreter should be giving you a full traceback of the exception; the first thing you need to do is find this. It could be occurring in one of two situations. (This is for single-threaded programs; I'm assuming your program is not multithreaded.)
During the execution of your program, in which case the program will be terminated by the exception, or
During finalization of objects (in their __del__(self) functions) in which case the error will be printed to stderr.
In both cases there should be a stack trace, not just the error message; I've confirmed that at least on Python ≥3.4 a stack trace is printed out for case 2.
You then need to follow this stack trace to see where the problem lies. Remember that the names you give to except ... are variables (even things like TypeError) that can be reassigned, so that you could conceivably be dealing with a (perverse) situation like:
TypeError = False
try:
...
except TypeError:
...
But more likely it will be something obvious such as:
class MyException: # Doesn't inherit from Exception
...
try:
...
except MyException:
...
There is one special case you need to be aware of: if you are seeing messages to stderr (case "2. During finalization," above) printed out as your program exits that means that the exception was thrown during cleanup as the interpreter shuts down, where random variables throughout the program may have already been set to None as part of the cleanup process. But in this case your program should still exit successfully.
I have test cases defined in an Excel sheet. I am reading a string from this sheet (my expected result) and comparing it to a result I read from a database (my actual result). I then use AssertEquals(expectedResult, actualResult) which prints any errors to a log file (i'm using log4j), e.g. I get java.lang.AssertionError: Different output expected:<10> but was:<7> as a result.
I now need to write that result into the Excel sheet (the one that defines the test cases). If only AssertEquals returned String, with the AssertionError text that would be great, as I could just write that immediately to my Excel sheet. Since it returns void though I got stuck.
Is there a way I could read the AssertionError without parsing the log file?
Thanks.
I think you're using junit incorrectly here. THis is why
assertEquals not AssertEquals ( ;) )
you shouldnt need to log. You should just let the assertions do their job. If it's all green then you're good and you dont need to check a log. If you get blue or red (eclipse colours :)) then you have problems to look at. Blue is failure which means that your assertions are wrong. For example you get 7 but expect 10. Red means error. You have a null pointer or some other exception that is throwing while you are running
You should need to read from an excel file or databse for the unit tests. If you really need to coordinate with other systems then you should try and stub or mock them. With the unit test you should work on trying to testing the method in code
if you are bootstrapping on JUnit to try and compare an excel sheet and database then I would ust export the table in excel as well and then just do a comparison in excel between columns
Reading from/writing to files is not really what tests should be doing. The input for the tests should be defined in the test, not in the external file which can change - this can either introduce false negatives or even worse false positives (making your tests effectively useless while also giving false confidence that everything is ok because tests are green).
Given your comment (a loop with 10k different parameters coming from file), I would recommend converting this excel file into JUnit Parameterized test. You may want to put the array definition in another class, because 10k lines is quite a lot.
If it is some corporate bureaucracy, and you need to have this excel file, then it makes sense to not write a classic "test". I would recommend just a main method that does the job - reads the file, runs the code, checks the output using simple if (output.equals(expected)) and then writes back to file.
Wrap your AssertEquals(expectedResult, actualResult) with try catch
in catch
catch(AssertionError e){
//deal with e.getMessage or etc.
}
But it not good idea for some reasons, I guess.
And try google something like soft assert
Documentation on assertEquals is pretty clear on what the method does:
Asserts that two objects are equal. If they are not, an AssertionError
without a message is thrown.
You need to wrap the assertion with try-catch block and in the exception handling do Your logging. You will need to make Your own message using the information from the specific test case, but this what You asked for.
Note:
If expected and actual are null, they are considered equal.
I am testing a software component and want that software to throw an Exception in certain situations.
I want to reproduce these situations by using the robot framework.
The testcase shall succeed if I catch a specific Exception (which I am expecting, because I am deliberately creating an error-state in my component under test)
The testcase shall fail if I do not receive the specific Exception (i.e. my component under test did not fail(throw an exception) in an error situation)
What I am looking for is something like this:
prepareErrorInTestEnvironment
try
executeComponentWhichThrowsException
except
pass
fail
Treatment of "expected exception" are a bit specific in Robot Framework as usually exception will fail the keyword and hence the test.
The keyword you are looking for is Run Keyword and Expect Error.
Your test would look like
*** Test Cases ***
my test
prepareErrorInTestEnvironment
Run Keyword and Expect Error TheExceptionYouExpect executeComponentWhichThrowsException
This will success if you get the proper exception, and fail otherwise
I believe try/else is what you want
prepareErrorInTestEnvironment
try:
executeComponentWhichThrowsException
except:
pass
else:
fail
Also you can return on except so fail will not execute:
prepareErrorInTestEnvironment
try:
executeComponentWhichThrowsException
except:
*dosomething*
return
fail
For example, in the case of "The array index out of bound" exception, why don't we check the array length in advance:
if(array.length < countNum)
{
//logic
}
else
{
//replace using exception
}
My question is, why choose to use an exception? and when to use an exception, instead of if-else
Thanks.
It depends on acceptable practices for a given language.
In Java, the convention is to always check conditions whenever possible and not to use exceptions for flow control. But, for example, in Python not only using exception in this manner is acceptable, but it is also a preferred practice.
They are used to inform the code that calls your code an exceptional condition occurred. Exceptions are more expensive than well formed if/else logic so you use them in exceptional circumstances such as reaching a condition in your code you cannot handle locally, or to support giving the caller of your code the choice of how to handle the error condition.
Usually if you find yourself throwing and catching exceptions in your own function or method, you can probably find a more efficient way of doing it.
There are many answers to that question. As a single example, from Java, when you are using multiple threads, sometimes you need to interrupt a thread, and the thread will see this when an InterruptedException is thrown.
Other times, you will be using an API that throws certain exceptions. You won't be able to avoid it. If the API throws, for example, an IOException, then you can catch it, or let it bubble up.
Here's an example where it would actually be better to use an exception instead of a conditional.
Say you had a list of 10,000 strings. Now, you only want those items which are integers. Now, you know that a very small number of them won't be integers (in string form). So should you check to see if every string is an integer before trying to convert them? Or should you just try to convert them and throw and catch an exception if you get one that isn't an integer? The second way is more efficient, but if they were mostly non-integers then it would be more efficient to use an if-statement.
Most of the time, however, you should not use exceptions if you can replace them with a conditional.
As someone has already said, 'Exceptions' in programming languages are for exceptional cases and not to set logical flow of your program. For example, in the case of given code snippet of your question, you have to see what the enclosing method's or function's intention is. Is checking array.length < countNum part of the business logic or not. If yes, then putting a pair of if/else there is the way to go. If that condition is not part of the business logic and the enclosing method's intention is something else, then write code for that something else and throw exception instead of going the if/else way. For example you develop an application for a school and in your application you have a method GetClassTopperGrades which is responsible for the business logic part which requires to return the highest marks of the student in a certain class. the method/function definition would be something like this:
int GetClassTopperGrades(string classID)
In this case the method's intention is to return the grades, for a valid class, which will always be a positive integer, according to the business logic of the application. Now if someone calls your method and passes a garbage string or null, what should it do? If should throw an exception e.g. ArgumentException or 'ArgumentNullException' because this was an exceptional case in this particular context. The method assumed that always a valid class ID will be passed and NULL or empty string is NOT a valid class ID (a deviation from the business logic).
Apart from that, in some conditions there is no prior knowledge about the outcome of a given code and no defined way to prevent an exceptional situation. For example, querying some remote database, if the network goes down, you don't have any other option there apart from throwing an exception. Would you check network connectivity before issuing every SQL query to the remote database?
There is strong and indisputable reason why to use exceptions - no matter of language. I strongly believe that decision about if to use exceptions or not have nothing to do with particular language used.
Using exceptions is universal method to notify other part of code that something wrong happened in kind of loosely coupled way. Let imagine that if you would like to handle some exceptional condition by using if.. nad else.. you need to insert into different part of your code some arbitrary variables and other stuff which probably would easily led to have spaghetti code soon after.
Let next imagine that you are using any external library/package and it's author decided to put in his/her code other arbitrary way to handle wrong states - it would force you to adjust to its way of dealing with it - for example you would need to check if particular methods returns true or false or whatever. Using exceptions makes handling errors much more easy - you just assume that if something goes wrong - the other code will throw exception, so you just wrap the code in try block and handle possible exception on your own way.
I have been doing some work with python-couchdb and desktopcouch. In one of the patches I submitted I wrapped the db.update function from couchdb. For anyone that is not familiar with python-couchdb the function is the following:
def update(self, documents, **options):
"""Perform a bulk update or insertion of the given documents using a
single HTTP request.
>>> server = Server('http://localhost:5984/')
>>> db = server.create('python-tests')
>>> for doc in db.update([
... Document(type='Person', name='John Doe'),
... Document(type='Person', name='Mary Jane'),
... Document(type='City', name='Gotham City')
... ]):
... print repr(doc) #doctest: +ELLIPSIS
(True, '...', '...')
(True, '...', '...')
(True, '...', '...')
>>> del server['python-tests']
The return value of this method is a list containing a tuple for every
element in the `documents` sequence. Each tuple is of the form
``(success, docid, rev_or_exc)``, where ``success`` is a boolean
indicating whether the update succeeded, ``docid`` is the ID of the
document, and ``rev_or_exc`` is either the new document revision, or
an exception instance (e.g. `ResourceConflict`) if the update failed.
If an object in the documents list is not a dictionary, this method
looks for an ``items()`` method that can be used to convert the object
to a dictionary. Effectively this means you can also use this method
with `schema.Document` objects.
:param documents: a sequence of dictionaries or `Document` objects, or
objects providing a ``items()`` method that can be
used to convert them to a dictionary
:return: an iterable over the resulting documents
:rtype: ``list``
:since: version 0.2
"""
As you can see, this function does not raise the exceptions that have been raised by the couchdb server but it rather returns them in a tuple with the id of the document that we wanted to update.
One of the reviewers went to #python on irc to ask about the matter. In #python they recommended to use sentinel values rather than exceptions. As you can imaging just an approach is not practical since there are lots of possible exceptions that can be received. My questions is, what are the cons of using Exceptions over sentinel values besides that using exceptions is uglier?
I think it is ok to return the exceptions in this case, because some parts of the update function may succeed and some may fail. When you raise the exception, the API user has no control over what succeeded already.
Raising an Exception is a notification that something that was expected to work did not work. It breaks the program flow, and should only be done if whatever is going on now is flawed in a way that the program doesn't know how to handle.
But sometimes you want to raise a little error flag without breaking program flow. You can do this by returning special values, and these values can very well be exceptions.
Python does this internally in one case. When you compare two values like foo < bar, the actual call is foo.__lt__(bar). If this method raises an exception, program flow will be broken, as expected. But if it returns NotImplemented, Python will then try bar.__ge__(foo) instead. So in this case returning the exception rather than raising it is used to flag that it didn't work, but in an expected way.
It's really the difference between an expected error and an unexpected one, IMO.
exceptions intended to be raised. It helps with debugging, handling causes of the errors and it's clear and well-established practise of other developers.
I think looking at the interface of the programme, it's not clear what am I supposed to do with returned exception. raise it? from outside of the chain that actually caused it? it seems a bit convoluted.
I'd suggest, returning docid, new_rev_doc tuple on success and propagating/raising exception as it is. Your approach duplicates success and type of 3rd returned value too.
Exceptions cause the normal program flow to break; then exceptions go up the call stack until they're intercept, or they may reach the top if they aren't. Hence they're employed to mark a really special condition that should be handled by the caller. Raising an exception is useful since the program won't continue if a necessary condition has not been met.
In languages that don't support exceptions (like C) you're often forced to check return values of functions to verify everything went on correctly; otherwise the program may misbehave.
By the way the update() is a bit different:
it takes multiple arguments; some may fail, some may succeed, hence it needs a way to communicate results for each arg.
a previous failure has no relation with operations coming next, e.g. it is not a permanent error
In that situation raising an exception would NOT be usueful in an API. On the other hand, if the connection to the db drops while executing the query, then an exception is the way to go (since it's a permament error and would impact all operations coming next).
By the way if your business logic requires all operations to complete successfully and you don't know what to do when an update fails (i.e. your design says it should never happen), feel free to raise an exception in your own code.