I am trying to find complete documentation for cursor.fetchone and all I can find is:
http://mysql-python.sourceforge.net/MySQLdb-1.2.2/public/MySQLdb.cursors.CursorStoreResultMixIn-class.html#fetchone
my questions are:
what is exactly returned? a normal python array?
what does it return if there no more rows?
what does it do if the connection is dropped? throw an error? have a unique return value?
I am not sure why I can't find real documentation on this. Thank you in advance
I'll try to answer in order your questions.
What is exactly returned?
A tuple or a dictionary, depending how you did the connection.
What does it return if there no more rows?
None
What does it do if the connection is dropped?
An Exception is raised. If it's due to a timeout, for instance, it will be a MySQLdb.OperationalError.
I am not sure why I can't find real documentation on this
Try here: https://mysqlclient.readthedocs.io/
Related
(Possibly a duplicate of Can't send a keyedMessage to brokers with partitioner.class=kafka.producer.DefaultPartitioner, although the OP of that question didn't mention kafka-python. And anyway, it never got an answer.)
I have a Python program that has been successfully (for many months) sending messages to the Kafka broker, using essentially the following logic:
producer = kafka.KafkaProducer(bootstrap_servers=[some_addr],
retries=3)
...
msg = json.dumps(some_message)
res = producer.send(some_topic, value=msg)
Recently, I tried to upgrade it to send messages to different partitions based on a definite key value extracted from the message:
producer = kafka.KafkaProducer(bootstrap_servers=[some_addr],
key_serializer=str.encode,
retries=3)
...
try:
key = some_message[0]
except:
key = None
msg = json.dumps(some_message)
res = producer.send(some_topic, value=msg, key=key)
However, with this code, no messages ever make it out of the program to the broker. I've verified that the key value extracted from some_message is always a valid string. Presumably I don't need to define my own partitioner, since, according to the documentation:
The default partitioner implementation hashes each non-None key using the same murmur2 algorithm as the java client so that messages with the same key are assigned to the same partition.
Furthermore, with the new code, when I try to determine what happened to my send by calling res.get (to obtain a kafka.FutureRecordMetadata), that call throws a TypeError exception with the message descriptor 'encode' requires a 'str' object but received a 'unicode'.
(As a side question, I'm not exactly sure what I'd do with the FutureRecordMetadata if I were actually able to get it. Based on the kafka-python source code, I assume I'd want to call either its succeeded or its failed method, but the documentation is silent on the point. The documentation does say that the return value of send "resolves to" RecordMetadata, but I haven't been able to figure out, from either the documentation or the code, what "resolves to" means in this context.)
Anyway: I can't be the only person using kafka-python 1.3.3 who's ever tried to send messages with a partitioning key, and I have not seen anything on teh Intertubes describing a similar problem (except for the SO question I referenced at the top of this post).
I'm certainly willing to believe that I'm doing something wrong, but I have no idea what that might be. Is there some additional parameter I need to supply to the KafkaProducer constructor?
The fundamental problem turned out to be that my key value was a unicode, even though I was quite convinced that it was a str. Hence the selection of str.encode for my key_serializer was inappropriate, and was what led to the exception from res.get. Omitting the key_serializer and calling key.encode('utf-8') was enough to get my messages published, and partitioned as expected.
A large contributor to the obscurity of this problem (for me) was that the kafka-python 1.3.3 documentation does not go into any detail on what a FutureRecordMetadata really is, nor what one should expect in the way of exceptions its get method can raise. The sole usage example in the documentation:
# Asynchronous by default
future = producer.send('my-topic', b'raw_bytes')
# Block for 'synchronous' sends
try:
record_metadata = future.get(timeout=10)
except KafkaError:
# Decide what to do if produce request failed...
log.exception()
pass
suggests that the only kind of exception it will raise is KafkaError, which is not true. In fact, get can and will (re-)raise any exception that the asynchronous publishing mechanism encountered in trying to get the message out the door.
I also faced the same error. Once I added json.dumps while sending the key, it worked.
producer.send(topic="first_topic", key=json.dumps(key)
.encode('utf-8'), value=json.dumps(msg)
.encode('utf-8'))
.add_callback(on_send_success).add_errback(on_send_error)
I am new to Java and I am having trouble understanding a question. I am asked to select which of the following choices throws an exception. The options are:
1.) Integer.parseInt(" ")
2.) Integer.parseInt("54 ")
3.) Integer.parseInt("")
4.) Integer.parseInt("-54")
5.) Integer.parseInt("54n")
To answer this question, I need some explanations. What does the Integer.parseInt method do? Doesn't it turn an integer into a String? What sort of arguments are illegal to put inside this method. For example, are you allowed to include negative numbers? Strings? Or does it only accept integers?
I was also wondering if you could clarify what "throws an exception" means. I have a rough idea, I think it just means that if there is an error in your program, it gets terminated. Howevere, you can use the "try-catch-finally" method to try and predicate any errors your program would have and write a possible code to fix it?
Sorry for all the questions, I just want to understand this completely.
I am new in scala programming, please consider the scenario...
.exec(http("request_7")
.post("/test/listing")
.headers(headers_12)
.formParam("abcId", "${abcID}")
.formParam("action_id", "100")
.formParam("controller", "/test/listing")
.check(jsonPath("$.data[*].xyzId").findAll.saveAs("xyzID"))
.check(jsonPath("$.data[*].abcNo").findAll.saveAs("ABCNo"))
.check(jsonPath("$.data[*].revId").findAll.saveAs("revID"))
.check(jsonPath("$.data[*].dTypeId").findAll.saveAs("dTypeID")))
In this request, I have to implement multiple check(s) to get the value. It is manual procedure.
Is there any method in scala to perform this scenario in single check? In other words,
I want to get these values in single json check. Is it possible???
So can anyone tell me what is the method to implement this scenario???
Your help would be much appreciated.
Thanks,
Praveen Mourya
Does anyone know the real difference between the two ways of type casting in Flex 3?
var myObject1:MyObject = variable as MyObject;
var myObject2:MyObject = MyObject(variable);
I prefer to use the second method because it will throw an Error when type cast fails, whereas the first method will just return null. But are there any other differences? Perhaps any advantages to using the first method?
The second type of casting has different behaviour for top level(http://livedocs.adobe.com/flex/2/langref/) types, e.g. Array(obj) does not cast in the straightforward way you describe; it creates a new Array if possible from obj, even if obj is an Array.
I'm sure the times this would cause unexpected behaviour would be rare but I always use "as" for this reason. It means if I do
int(str)
I know it's a cast in the "attempt to convert" sense of the word not in the "I promise it is" sense.
ref: got some confirmation on this from http://raghuonflex.wordpress.com/2007/07/27/casting-vs-the-as-operator/
The as method returns null if cast fails.
The () method throws and error if the cast fails.
If the value of variable is not compatible with MyObject, myObject1 will contain null and you will be surprised by a null pointer error (1009 : cannot access a property or method of a null object reference.) somewhere later in the program when you try to access it. Where as if you are casting using the MyObject(variable) syntax, you will get a type coercion error (1034 : Type Coercion failed: cannot convert _ to _) at the same line itself - which is more helpful than getting a 1009 somewhere later and wondering what went wrong.
I think I read somewhere on this site that as is slighty faster than (), but I can't find the question again.
Beside that this question have been asked many times, you will find an more in-depth answer here.
I recently discovered the very useful [] tag when searching on StackOverflow, it allows to only search in questions tagged with the specified tag(s). So you could do a search like [actionscript-3] as vs cast. There are more search tips here: https://stackoverflow.com/search.
And no; the irony in that I can not find the question about performance and write about how to search is not lost on me ;)
I think as returns back the base class and not null when the casting fails and () throws an error.
I'm rewriting a series of PHP functions to a container class. Many of these functions do a bit of processing, but in the end, just echo content to STDOUT.
My question is: should I have a return value within these functions? Is there a "best practice" as far as this is concerned?
In systems that report errors primarily through exceptions, don't return a return value if there isn't a natural one.
In systems that use return values to indicate errors, it's useful to have all functions return the error code. That way, a user can simply assume that every single function returns an error code and develop a pattern to check them that they follow everywhere. Even if the function can never fail right now, return a success code. That way if a future change makes it possible to have an error, users will already be checking errors instead of implicitly silently ignoring them (and getting really confused why the system is behaving oddly).
Can the processing fail? If so, should the caller know about that? If either of these is no, then I don't see value in a return. However, if the processing can fail, and that can make a difference to the caller, then I'd suggest returning a status or error code.
Do not return a value if there is no value to return. If you have some value you need to convey to the caller, then return it but that doesn't sound like the case in this instance.
I will often "return: true;" in these cases, as it provides a way to check that the function worked. Not sure about best practice though.
Note that in C/C++, the output functions (including printf()) return the number of bytes written, or -1 if this fails. It may be worth investigating this further to see why it's been done like this. I confess that
I'm not sure that writing to stdout could practically fail (unless you actively close your STDOUT stream)
I've never seen anyone collect this value, let alone do anything with it.
Note that this is distinct from writing to file streams - I'm not counting stream redirection in the shell.
To do the "correct" thing, if the point of the method is only to print the data, then it shouldn't return anything.
In practice, I often find that having such functions return the text that they've just printed can often be useful (sometimes you also want to send an error message via email or feed it to some other function).
In the end, the choice is yours. I'd say it depends on how much of a "purist" you are about such things.
You should just:
return;
In my opinion the SRP (single responsibility principle) is applicable for methods/functions as well, and not only for objects. One method should do one thing, if it outputs data it shouldn't do any data processing - if it doesn't do processing it shouldn't return data.
There is no need to return anything, or indeed to have a return statement. It's effectively a void function, and it's comprehensible enough that these have no return value. Putting in a 'return;' solely to have a return statement is noise for the sake of pedantry.