I am using a large list in my python script and need to access the last value of this list very often, while the list doesn't change that much. Should I simply access it directly (longList[-1]) or is it preferable to assign the last value of the list to a variable (lastValue = longList[-1]) and use this variable instead. Of course I have to update the variable when the list changes.
From a functionality point of few it is the same, I am more concerned about the performance gain it could bring.
List access takes O(1) time. So, there is no need to assign it to a variable.
Related
When you open the print dialog of an editor, you typically get a field for specifying which pages you want to print - which can be multiple ranges, e.g.: "5,11,31-33"
Now, there are other scenarios in which this kind of input from a user is relevant - especially in configuration files for sequential or iterative processes where you want to qualify which iterations or elements a certain action or feature should apply to.
However, I'm not aware of a name for this kind of strings; nor of an accepted standard format/convention for them (i.e. can you add spaces? Can you use semicolons instead of commas? Must the ranges be sorted? Are overlaps allowed and are they maintained or discarded? Can ranges use ".." instead of "-"? Can you range down instead of up? etc.).
Is there some such convention or such standard?
My motivation is double: I need to parse such ranges in a piece of code I'm looking at, any I want both to do it correctly (or rather per-convention), and secondly to go look for parsing functionality in existing libraries. Right now I don't even have a name to go on.
I need to use redis in golang as cache and store a array of structs in it. Since redis allows only storing array of strings(correct me if I'm wrong), I'll marshal the items in my array. Was wondering shall I use redis list where I'm storing marshaled structs in string format OR I can just marshal the whole array and store as key<>value in redis and not use list. One pro of using list is I can fetch ranged items from the list but scale is not the problem here since I'll be storing less than 100 items in the list. What else should I consider here.
Thankyou!!
The answer depends of how you want to use redis
For instance, store one struct using json (or any kind of serialization) and store it in a single position is easy to read / write.
But if you need to efficiently retrieve/ update one field, you can save it in a different way. However this scenario is pretty rare and complex to handle.
For instance you need to be sure you write always in the same order, to calculate the right offset. If you need to add a new field, will be really difficult to be 100% backward compatible. You probably need to create a new type (like a version 2).
I added a linked fact using:
context.InsertLinked(longOrderKey, longOrder);
At some point later, I want to remove this fact. It's easy for me to construct the key without having the record:
var longOrderKey = (managedAccount.AccountId, PositionType.Long, fungible.FungibleId);
So why do I need the record when removing a linked fact using the method:
context.RetractLinked(longOrderKey, longOrder);
Why can't this method just use the longOrderKey? What if I don't have the 'longOrder' record. Do I really need to look it up before I can remove it?
Linked facts are tied to an activation that created them. The purpose of the key is to be able to identify the specific fact if the activation produced more than one linked fact. If you are inserting just one linked fact in the RHS of a rule, you can really set the key to anything, e.g. "1"; if you were to insert two facts, you could set keys to "1" and "2", and so on. In essence, the key is to identify the linked fact within the activation. The fact itself is needed, so that the engine can find the corresponding entries in the working memory. Much like ISession.Retract requires the fact object, so that it can find it in the working memory.
Another point is that in most scenarios you should not need to retract the linked facts as they would get retracted automatically, once the activation gets deleted (i.e. the conditions that created the activation become false).
I want to write a TIBasic program for the nspire CS CAS which will perform simple finite element analysis. In order to do this, I need to be able to input a non-specific number of variables since the number of members in a problem will vary.
Is there a command or trick I can use to program variables k1,k2,k3,...,kn?
Unfortunately, I don't think there's a way to use multiple variables like that. You might be able to use a list and store all your variables there. Lists can only hold up to 999 elements though, so that'll limit what you can do.
I'm currently working with JMeter in order to stress test one of our systems before release. Through this, I need to simulate users clicking links on the webpage presented to them. I've decided to extract theese links with an XPath Post-Processor.
Here's my problem:
I have an a XPath expression that looks something like this:
//div[#data-attrib="foo"]//a//#href
However I need to extract a specific child for each thread (user). I want to do something like this:
//div[#data-attrib="foo"]//a[position()=n]//#href
(n being the current index)
My question:
Is there a way to make this query work, so that I'm able to extract a new index of the expression for each thread?
Also, as I mentioned, I'm using JMeter. JMeter creates a variable for each of the resulting nodes, of an XPath query. However it names them as "VarName_n", and doesn't store them as a traditional array. Does anyone know how I can dynamicaly pick one of theese variables, if possible? This would also solve my problem.
Thanks in advance :)
EDIT:
Nested variables are apparently not supported, so in order to dynamically refer to variables that are named "VarName_1", VarName_2" and so forth, this can be used:
${__BeanShell(vars.get("VarName_${n}"))}
Where "n" is an integer. So if n == 1, this will get the value of the variable named "VarName_1".
If the "n" integer changes during a single thread, the ForEach controller is designed specifically for this purpose.
For the first question -- use:
(//div[#data-attrib="foo"]//a)[position()=$n]/#href
where $n must be substituted with a specific integer.
Here we also assume that //div[#data-attrib="foo"] selects a single div element.
Do note that the XPath pseudo-operator // typically result in very slow evaluation (a complete sub-tree is searched) and also in other confusing problems ( this is why the brackets are needed in the above expression).
It is recommended to avoid using // whenever the structure of the document is known and a complete, concrete path can be specified.
As for the second question, it is not clear. Please, provide an example.