I came across this bit of code:
n = args[0] as Long
[*n..1, n].any{ println ' '*it + '*'*(n - ~n - it*2) }
It's used for printing a tree form of structure. Like this:
*
***
*****
*******
*
(for n=4)
How does the code [*n..1,n] produce [4, 3, 2, 1, 4]?
How does any method works here? The Doc doesn't help me much. What is a predictive that can be passed to any(as mentioned in Doc's)?
Whats the use of any and how its handled in this case?
Q1a: * "unpacks" an array. .. creates a range. [] creates a collection.
Q1b: *n..1 unpacks [4,3,2,1] into its individual parts.
Q1c: [4,3,2,1,n] == [4,3,2,1,4]
Q2: I don't know why any was used here; each works just as well, and makes more sense in context. any does loop over the connection, so the println side-effect functions as intended.
Normally any would be used to determine if any collection elements met a criteria, for example:
[*n..1,n].any { it > 10 } // Returns false, no elements are > 10
[*n..1,n].any { it == 3 } // Returns true, because at least one element is 3
The last statement of the closure is used to determine if each item meets the criteria. println returns null, so any will return false. The value is unused and discarded.
The only reason I can think of that someone might have used any is to avoid seeing the return value of each in the console. each returns the original collection.
1) n..1 is called a range literal, it creates a groovy.lang.Range object that decrements by 1 from n to 1. This is then merged into the surrounding list context using the "Spread operator (*)"
2) the any method is defined in DefaultGroovyMethods and it is a predicate function that returns true if an element in a collection satisfies the supplied predicate closure. In this example, the code doesn't check the return value, so original other could have produced the same output using an each call instead.
Related
I'm trying to port code from DML 1.2 to DML 1.4. Here is part of code that i ported:
group rx_queue [i < NQUEUES] {
<...>
param desctype = i < 64 #? regs.SRRCTL12[i].DESCTYPE.val #: regs.SRRCTL2[i - 64].DESCTYPE.val; // error occurs here
<...>
}
Error says:
error: non-constant expression: cast(i, int64 ) < 64
How can i specify parameter dependent on index value?
I tried to use if...else instead ternary operator, but it says that conditional parameters are not allowed in DML.
Index parameters in DML are a slightly magical expressions; when used from within parameters, they can evaluate to either a constant or a variable depending on where the parameter is used from. Consider the following example:
group g[i < 5] {
param x = i * 4;
method m() {
log info: "%d", x;
log info: "%d", g[4 - i].x;
log info: "%d", g[2].x;
}
}
i becomes an implicit local variable within the m method, and in params, indices are a bit like implicit macro parameters. When the compiler encounters x in the first log statement, the param will expand to i * 4 right away. In the second log statement, the x param is taken from an object indexed with the expression 4 - i, so param expansion will instead insert (5 - i) * 4. In the third log statement, the x param is taken from a constant indexed object, so it expands to 2 * 4 which collapses into the constant 8.
Most uses of desctype will likely happen from contexts where indices are variable, and the #? expression requires a constant boolean as condition, so this will likely give an error as soon as anyone tries to use it.
I would normally advise you to switch from #? to ? in the definition of the desctype param, but that fails in this particular case: DMLC will report error: array index out of bounds on the i - 64 expression. This error is much more confusing, and happens because DMLC automatically evaluates every parameter once with all zero indices, to smoke out misspelled identifiers; this will include evaluation of SRRCTL2[i-64] which collapses into SRRCTL2[-64] which annoys DMLC.
This is arguably a compiler bug; DMLC should probably be more tolerant in this corner. (Note that even if we would remove the zero-indexed validation step from the compiler, your parameter would still give the same error message if it ever would be explicitly referenced with a constant index, like log info: "%d", rx_queue[0].desctype).
The reason why you didn't get an error in DML 1.2 is that DML 1.2 had a single ternary operator ? that unified 1.4's ? and #?; when evaluated with a constant condition the dead branch would be disregarded without checking for errors. This had some strange effects in other situations, but made your particular use case work.
My concrete advise would be to replace the param with a method; this makes all index variables unconditionally non-constant which avoids the problem:
method desctype() -> (uint64) {
return i < 64 ? regs.SRRCTL12[i].DESCTYPE.val : regs.SRRCTL2[i - 64].DESCTYPE.val;
}
I'm kind of newbie as programmer, but I wish to master Python and I'm developing open source application. This application has function to gather some information. This function takes 1 parameter. This parameter can be 0, 1 or 2. 0 = False, 1 = True, 2 = Multi. Also I have an if statement that does 2 actions. 1st - (when False) gathers single type value, 2nd - (when True) gathers multiple type values and when parameter is 2 (multi) then it will gather single type (1st) and multiple types (2nd). My if statement looks like this:
if False:
get_single_type = code.of.action
generators.generate_data(False, get_single_type)
elif True:
get_multiple_type = code.of.action
generators.generate_data(True, get_multiple_type)
else:
get_single_type = code.of.action
generators.generate_data(False, get_single_type)
get_multiple_type = code.of.action
generators.generate_data(True, get_multiple_type)
Is there maybe better way of avoiding this kind of coding, like in last else statement when I call both single and multiple.
Thank you in advance.
One thing I learned from Python is that although it lacks the Switch operator, you can use dictionary in a similar fashion to get things done since everything is an object:
def get_single():
# define your single function
get_single_type = code.of.action
generators.generate_data(False, get_single_type)
def get_multi():
# define your multi function
get_multiple_type = code.of.action
generators.generate_data(True, get_multiple_type)
actions = {
0: [get_single],
1: [get_multi],
2: [get_single, get_multi]
}
parameter = 0 # replace this line with however you are capturing the parameter
for action in actions[parameter]:
action()
This way you avoid c+p your code everywhere and have it referenced from the function, and your "actions" dictionary define the function to be used based on the parameter given.
In this case since you have multiple functions you want to call, I kept all dictionary items as a list so the structure is consistent and it can be iterated through to perform any number of actions.
Ensure you use leave out the () in the dictionary so that the functions aren't instantiated when the dictionary is defined. And remember to add () when you are actually calling the function from the dictionary to instantiate it.
This is something you will often encounter and it is pretty much always bad practice to be repeating code. Anyway, the way to do this is use two if-statements. This way, even if the first case passes, the second case can still pass. Oh, and assuming your variable that can be 0, 1 or 2 is called x, then we could either use or and two checks:
if x == 0 or x == 2:
but, personally, I prefer using in on a tuple:
if x in (0, 2):
get_single_type = code.of.action
generators.generate_data(False, get_single_type)
if x in (1, 2):
get_multiple_type = code.of.action
generators.generate_data(True, get_multiple_type)
I am interested in creating a list / array of functions "G" consisting of many small functions "g". This essentially should correspond to a series of functions 'evolving' in time.
Each "g" takes-in two variables and returns the product of these variables with an outside global variable indexed at the same time-step.
Assume obs_mat (T x 1) is a pre-defined global array, and t corresponds to the time-steps
G = []
for t in range(T):
# tried declaring obs here too.
def g(current_state, observation_noise):
obs = obs_mat[t]
return current_state * observation_noise * obs
G.append(g)
Unfortunately when I test the resultant functions, they do not seem to pick up on the difference in the obs time-varying constant i.e. (Got G[0](100,100) same as G[5](100,100)). I tried playing around with the scope of obs but without much luck. Would anyone be able to help guide me in the right direction?
This is a common "gotcha" to referencing variables from an outer scope when in an inner function. The outer variable is looked up when the inner function is run, not when the inner function is defined (so all versions of the function see the variable's last value). For each function to see a different value, you either need to make sure they're looking in separate namespaces, or you need to bind the value to a default parameter of the inner function.
Here's an approach that uses an extra namespace:
def make_func(x):
def func(a, b):
return a*b*x
return func
list_of_funcs = [make_func(i) for i in range(10)]
Each inner function func has access to the x parameter in the enclosing make_func function. Since they're all created by separate calls to make_func, they each see separate namespaces with different x values.
Here's the other approach that uses a default argument (with functions created by a lambda expression):
list_of_funcs = [lambda a, b, x=i: a*b*x for i in range(10)]
In this version, the i variable from the list comprehension is bound to the default value of the x parameter in the lambda expression. This binding means that the functions wont care about the value of i changing later on. The downside to this solution is that any code that accidentally calls one of the functions with three arguments instead of two may work without an exception (perhaps with odd results).
The problem you are running into is one of scoping. Function bodies aren't evaluated until the fuction is actually called, so the functions you have there will use whatever is the current value of the variable within their scope at time of evaluation (which means they'll have the same t if you call them all after the for-loop has ended)
In order to see the value that you would like, you'd need to immediately call the function and save the result.
I'm not really sure why you're using an array of functions. Perhaps what you're trying to do is map a partial function across the time series, something like the following?
from functools import partial
def g(current_state, observation_noise, t):
obs = obs_mat[t]
return current_state * observation_noise * obs
g_maker = partial(g, current, observation)
results = list(map(g_maker, range(T)))
What's happening here is that partial creates a partially-applied function, which is merely waiting for its final value to be evaluated. That final value is dynamic (but the first two are fixed in this example), so mapping that partially-applied function over a range of values gets you answers for each value.
Honestly, this is a guess because it's hard to see what else you are trying to do with this data and it's hard to see what you're trying to achieve with the array of functions (and there are certainly other ways to do this).
The issue (assuming that your G.append call is mis-indented) is simply that the name t is mutated when you loop over the iterator returned by range(T). Since every function g you create stores returns the same name t, they wind up all returning the same value, T - 1. The fix is to de-reference the name (the simplest way to do this is by sending t into your function as a default value for an argument in g's argument list):
G = []
for t in range(T):
def g(current_state, observation_noise, t_kw=t):
obs = obs_mat[t_kw]
return current_state * observation_noise * obs
G.append(g)
This works because it creates another name that points at the value that t references during that iteration of the loop (you could still use t rather than t_kw and it would still just work because tg is bound to the value that tf is bound to - the value never changes, but tf is bound to another value on the next iteration, while tg still points at the "original" value.
So I was getting a notice in my php while creating a google product feed.
The notice was
"The following php notice has occurred 4989 times on the _ site today:
PHP Notice: Undefined index: 0 in /xxx/Status.php on line 583"
This was the code in that class
public function inStockLocally($productcode)
{
if($this->_status[$productcode]['status'] == self::IN_STOCK) {
return $this->_status[$productcode]['in_stock_local'];
}
return false;
}
The function was getting a $productcode = 0, but the productcode was infact 'w32', so the key didn't exist.
up the stack where the function was being called I put this in, in order to break on the troublesome product.
if ($productcode == 0) {
$test = 'breakhere';
}
Using netbeans and firebug, it broke on the line when $productcode = 'w32'
So my question is why does 'w32' == 0 evaluate to true?
It is also evaluating to true with other similar structure codes like 'h94'.
Any help would be appreciated as no one in the department can figure out why this is happening.
I guess I didn't put enough info in the q. Two things going on.
1. 'w32' converted to a number = 0 for some reason. 2. [0] is being inserted as my key in the array when the productcode has the structure 'x##';
I'm a little new here, so pardon if this isn't the answer you were expecting, but PHP does a lot of automatic type conversion. So any string that doesn't start with a numeric character (0..9, +, -, etc) will evaluate to zero.
"If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. "
http://php.net/manual/en/language.operators.comparison.php
Additionally, I suppose you have an indexed array, although you expect it to be an associative array:
The array() function is used to create an array.
In PHP, there are three types of arrays:
Indexed arrays - Arrays with numeric index
Associative arrays - Arrays with named keys
Multidimensional arrays - Arrays containing one or more arrays
Syntax
Syntax for indexed arrays:
array(value1,value2,value3,etc.);
Syntax for associative arrays:
array(key=>value,key=>value,key=>value,etc.);
I am new to groovy and I've been facing some issues understanding the each{} and eachwithindex{} statements in groovy.
Are each and eachWithIndex actually methods? If so what are the arguments that they take?
In the groovy documentation there is this certain example:
def numbers = [ 5, 7, 9, 12 ]
numbers.eachWithIndex{ num, idx -> println "$idx: $num" } //prints each index and number
Well, I see that numbers is an array. What are num and idx in the above statement? What does the -> operator do?
I do know that $idx and $num prints the value, but how is it that idx and num are automatically being associated with the index and contents of the array? What is the logic behind this? Please help.
These are plain methods but they follow quite a specific pattern - they take a Closure as their last argument. A Closure is a piece of functionality that you can pass around and call when applicable.
For example, method eachWithIndex might look like this (roughly):
void eachWithIndex(Closure operation) {
for (int i = 0; this.hasNext(); i++) {
operation(this.next(), i); // Here closure passed as parameter is being called
}
}
This approach allows one to build generic algorithms (like iteration over items) and change the concrete processing logic at runtime by passing different closures.
Regarding the parameters part, as you see in the example above we call the closure (operation) with two parameters - the current element and current index. This means that the eachWithIndex method expects to receive not just any closure but one which would accept these two parameters. From a syntax prospective one defines the parameters during closure definition like this:
{ elem, index ->
// logic
}
So -> is used to separate arguments part of closure definition from its logic. When a closure takes only one argument, its parameter definition can be omitted and then the parameter will be accessible within the closure's scope with the name it (implicit name for the first argument). For example:
[1,2,3].each {
println it
}
It could be rewritten like this:
[1,2,3].each({ elem ->
println elem
})
As you see the Groovy language adds some syntax sugar to make such constructions look prettier.
each and eachWithIndex are, amongst many others, taking so called Closure as an argument. The closure is just a piece of Groovy code wrapped in {} braces. In the code with array:
def numbers = [ 5, 7, 9, 12 ]
numbers.eachWithIndex{ num, idx -> println "$idx: $num" }
there is only one argument (closure, or more precisely: function), please note that in Groovy () braces are sometime optional. num and idx are just an optional aliases for closure (function) arguments, when we need just one argument, this is equivalent (it is implicit name of the first closure argument, very convenient):
def numbers = [ 5, 7, 9, 12 ]
numbers.each {println "$it" }
References:
http://groovy.codehaus.org/Closures
http://en.wikipedia.org/wiki/First-class_function
Normally, if you are using a functional programing language such as Groovy, you would want to avoid using each and eachWithIndex since they encourage you to modify state within the closure or do things that have side effects.
If possible, you may want to do your operations using other groovy collection methods such as .collect or .inject or findResult etc.
However, to use these for your problem, i.e print the list elements with their index, you will need to use the withIndex method on the original collection which will transform the collection to a collection of pairs of [element, index]
For example,
println(['a', 'b', 'c'].withIndex())
EachWithIndex can be used as follows:
package json
import groovy.json.*
import com.eviware.soapui.support.XmlHolder
def project = testRunner.testCase.testSuite.project
def testCase = testRunner.testCase;
def strArray = new String[200]
//Response for a step you want the json from
def response = context.expand('${Offers#Response#$[\'Data\']}').toString()
def json = new JsonSlurper().parseText(response)
//Value you want to compare with in your array
def offername = project.getPropertyValue("Offername")
log.info(offername)
Boolean flagpresent = false
Boolean flagnotpresent = false
strArray = json.Name
def id = 0;
//To find the offername in the array of offers displayed
strArray.eachWithIndex
{
name, index ->
if("${name}" != offername)
{
flagnotpresent= false;
}
else
{
id = "${index}";
flagpresent = true;
log.info("${index}.${name}")
log.info(id)
}
}