I wanna raise Exception under certain circumstances, say some if or case conditions. I'm doing this for returning some failure status if certain condition if not satisfied, so I could know and deal with that.
I have tried several methods but none could raise Exception only under some condition:
select some column does not exist: Exception is raised when parsing.
divide some value by 0: null is returned, instead of raising Exception
make some assertation in UDF: assertations are not allowed in UDF
I wonder if it's possible deliberately Exception to terminate the program.
e.g. (not legal HiveQL)
SELECT CASE some_condition WHEN true THEN continue ELSE exception END AS condition
Take a look at assert_true UDF, looks like it's exactly what you need.
hive> select assert_true (2<1);
OK
Failed with exception java.io.IOException:org.apache.hadoop.hive.ql.metadata.HiveException: ASSERT_TRUE(): assertion failed.
Time taken: 0.497 seconds
Related
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.
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.
Exception is not being caught with its name but it is caught when others keyword is used? Below is my code
p.ads
package p is
procedure proc ;
end p;
p.adb
package body p is
my_exp:exception; -- user define exception
procedure proc is
begin
raise my_exp; -- spreading exception
end proc;
end p;
p_main.adb
with p;
with ada.text_io;
use ada.text_io;
use p;
procedure p_main is
begin
proc;
exception
when my_exp=>put(" my_exp");-- error but when others is used then.its good why?
end p_main;
A/c to adacore site my_exp is not visible here then how it is visible when others keyword is used?
Your code has numerous syntax errors. It's always better to copy-and-paste your exact code into the question; you appear to have re-typed it, which makes it difficult to distinguish between typos and actual errors in your original code.
Ignoring the syntax errors, this:
exception
when my_exp => put(" my_exp");
fails to compile because the name my_exp is not visible. (If you want it to be visible it should be in the package specification, but that's not what you asked.)
If you replace when my_exp by when others, it works; the exception is handled. This is because a when others clause handles any exception that's been raised, whether its name is visible or not.
An exception is a condition that exists when a program is running. The exception handler detects and handles that run-time entity. It doesn't need to refer to it by whatever identifier you used to define it.
If the name my_exp had been visible, the handler still (almost certainly) wouldn't use the name to identify the exception. Instead, the compiler creates some run-time data structure that allows exceptions to be identified, perhaps by a reference to a specific memory address. The exact mechanism depends on the compiler, and understanding the details is not terribly important unless you're writing a compiler.
The run-time detection that an exception has been raised, and which exception it is, does not depend on the name you've assigned to the exception in your source code.
The reference to the name my_exp is rejected at compile time because that name is not visible at compile time.
The first thing to understand is that if your package can raise a custom exception which isn't advertised by the package specification, that is bad design because it leads to unpleasant surprises for the package users.
So the right thing to do is to declare my_exp in the package instead of hiding it in the body.
package p is
my_exp:exception; -- user define exception
procedure proc ;
end p;
And then fix all the other trivial syntax errors, and your program works as advertised.
But even if you don't, and "my_exp" is not visible in the main program, its exception handler can identify it correctly.
procedure p_main is
begin
proc;
end p_main;
./p_main
raised P.MY_EXP : p.adb:7
Or you can manipulate that information yourself, for better diagnostics or error recovery
with Ada.Exceptions; -- we need to process exception data
procedure p_main is
begin
proc;
exception
when E : others =>
put("something bad happened : " & Ada.Exceptions.Exception_Name(E));
end p_main;
./p_main
something bad happened : P.MY_EXP
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
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.