I have a jupyter notebook function
def add_args(a: int, b: int) -> int:
return a + b
a = sys.argv[1] # 0 is file name
b = sys.argv[2]
print("sum of {} and {} is {}".format(a, b, add_args(a, b)))
I want to execute this function from within notebook. I want to run only this function and it should print answer like this sum of 1 and 2 is 3.
Thank you.
Related
I have a function
f : a -> b -> ( a, c )
and I need to apply f to a list of b, while a is accumulated and c is appended to a list, getting ( a, List c ). I think the signature of what I want to do is
(a -> b -> ( a, c )) -> a -> List b -> ( a, List c )
The real scenario here is that I have
getThing : Model -> Thing -> ( Model, Cmd Msg )
and need to run getThing on a list of Thing, passing the Model to each call to getThing and returning the model and all Cmds that are to be performed in a Platform.Cmd.batch.
I think this problem should be broken down into multiple parts, but I am not sure where to start. It feels like using a fold is appropriate for the Model, but I need a map for the Cmd part.
You just need to unpack the tuple returned by getThing in each iteration of the fold, then pack it back up with the command added to the accumulated list of commands as the accumulator.
mapThings : (a -> b -> ( a, c )) -> a -> List b -> ( a, List c )
mapThings getThing initialModel things =
List.foldl
(\thing ( model, cmds ) ->
let
( newModel, cmd ) =
getThing model thing
in
( newModel, cmd :: cmds )
)
( initialModel, [] )
things
The naming here is very specific to help mnemonics, but it can easily be generalized just by using more generic variable names.
If you don't mind pulling in another package, there's elm-community/list-extra List.Extra.mapAccuml and List.Extra.mapAccumr
https://package.elm-lang.org/packages/elm-community/list-extra/latest/List-Extra#mapAccuml
I want to print out the elements in the list in reverse order recursively.
def f3(alist):
if alist == []:
print()
else:
print(alist[-1])
f3(alist[:-1])
I know it is working well, but I don't know the difference between
return f3(alist[:-1])
and
f3(alist[:-1])
Actually both are working well.
My inputs are like these.
f3([1,2,3])
f3([])
f3([3,2,1])
There is a difference between the two although it isn't noticeable in this program. Look at the following example where all I am doing is passing a value as an argument and incrementing it thereby making it return the value once it hits 10 or greater:
from sys import exit
a = 0
def func(a):
a += 1
if a >= 10:
return a
exit(1)
else:
# Modifications are made to the following line
return func(a)
g = func(3)
print(g)
Here the output is 10
Now if I re-write the code the second way without the "return" keyword like this :
from sys import exit
a = 0
def func(a):
a += 1
if a >= 10:
return a
exit(1)
else:
# Modifications are made to the following line
func(a)
g = func(3)
print(g)
The output is "None".
This is because we are not returning any value to handle.
In short, return is like internal communication within the function that can be possibly handled versus just running the function again.
I have a Julia function in a file. Let's say it is the below. Now I want to pass arguments into this function. I tried doing
julia filename.jl randmatstat(5)
but this gives an error that '(' token is unexpected. Not sure what the solution would be. I am also a little torn on if there is a main function / how to write a full solution using Julia. For example what is the starting / entry point of a Julia Program?
function randmatstat(t)
n = 5
v = zeros(t)
w = zeros(t)
for i = 1:t
a = randn(n,n)
b = randn(n,n)
c = randn(n,n)
d = randn(n,n)
P = [a b c d]
Q = [a b; c d]
v[i] = trace((P.'*P)^4)
w[i] = trace((Q.'*Q)^4)
end
std(v)/mean(v), std(w)/mean(w)
end
Julia doesn't have an "entry point" as such.
When you call julia myscript.jl from the terminal, you're essentially asking julia to execute the script and exit. As such, it needs to be a script. If all you have in your script is a function definition, then it won't do much unless you later call that function from your script.
As for arguments, if you call julia myscript.jl 1 2 3 4, all the remaining arguments (i.e. in this case, 1, 2, 3 and 4) become an array of strings with the special name ARGS. You can use this special variable to access the input arguments.
e.g. if you have a julia script which simply says:
# in julia mytest.jl
show(ARGS)
Then calling this from the linux terminal will give this result:
<bashprompt> $ julia mytest.jl 1 two "three and four"
UTF8String["1","two","three and four"]
EDIT: So, from what I understand from your program, you probably want to do something like this (note: in julia, the function needs to be defined before it's called).
# in file myscript.jl
function randmatstat(t)
n = 5
v = zeros(t)
w = zeros(t)
for i = 1:t
a = randn(n,n)
b = randn(n,n)
c = randn(n,n)
d = randn(n,n)
P = [a b c d]
Q = [a b; c d]
v[i] = trace((P.'*P)^4)
w[i] = trace((Q.'*Q)^4)
end
std(v)/mean(v), std(w)/mean(w)
end
t = parse(Int64, ARGS[1])
(a,b) = randmatstat(t)
print("a is $a, and b is $b\n")
And then call this from your linux terminal like so:
julia myscript.jl 5
You can try running like so:
julia -L filename.jl -E 'randmatstat(5)'
Add the following to your Julia file:
### original file
function randmatstat...
...
end
### new stuff
if length(ARGS)>0
ret = eval(parse(join(ARGS," ")))
end
println(ret)
Now, you can run:
julia filename.jl "randmatstat(5)"
As attempted originally. Note the additional quotes added to make sure the parenthesis don't mess up the command.
Explanation: The ARGS variable is defined by Julia to hold the parameters to the command running the file. Since Julia is an interpreter, we can join these parameters to a string, parse it as Julia code, run it and print the result (the code corresponds to this description).
I recently started learning F# and because I am quite new to most of the functional concepts I tend to want to write small examples for myself and check my premises with the results of the test.
Now I can't seem to be able to understand the result of the following code and why it behaves as such. The use case: I roll four six sides dice and only return their total when their sum is greater than 20.
This is my code:
let rnd = System.Random()
let d6 () = rnd.Next(1, 7)
let rec foo () =
// create a list of 4 d6 throws and print out the list
let numbers = seq { for i in 1 .. 4 -> d6() }
numbers |> Seq.iter( fun n -> printf "%i " n )
printfn "\n"
// sum the list and return the sum only when the sum is greater than 20
let total = numbers |> Seq.sum
match total with
| n when n < 21 -> foo ()
| _ -> total
Now when you run this you will find that this will eventually return a number greater than 20.
When you look at the output you will find that it did not print out the last list of numbers and I can't figure out why.
The sequences are lazily evaluated and are not cached. What happens here is that you have a sequence with a side effect that's evaluated multiple times.
First evaluation yields first sequence of random numbers:
numbers |> Seq.iter( fun n -> printf "%i " n )
The second call runs the evaluation again, producing completely different sequence:
let total = numbers |> Seq.sum
What you need to do if you want to keep the first evaluation around to run through it multiple times is either materialize the sequence or cache it:
// create a list directly
let numbers = [ for i in 1 .. 4 -> d6() ]
// or create a list from sequence
let numbers = seq { for i in 1 .. 4 -> d6() } |> List.ofSeq
// or cache the sequence
let numbers = seq { for i in 1 .. 4 -> d6() } |> Seq.cache
I defined a higher-order function like this:
val func : int -> string -> unit
I would like to use this function in two ways:
other_func (func 5)
some_other_func (fun x -> func x "abc")
i.e., by making functions with one of the arguments already defined. However, the second usage is less concise and readable than the first one. Is there a more readable way to pass the second argument to make another function?
In Haskell, there's a function flip for this. You can define it yourself:
let flip f x y = f y x
Then you can say:
other_func (func 5)
third_func (flip func "abc")
Flip is defined in Jane Street Core as Fn.flip. It's defined in OCaml Batteries Included as BatPervasives.flip. (In other words, everybody agrees this is a useful function.)
The question posed in the headline "change order of parameters" is already answered. But I am reading your description as "how do I write a new function with the second parameter fixed". So I will answer this simple question with an ocaml toplevel protocol:
# let func i s = if i < 1 then print_endline "Counter error."
else for ix = 1 to i do print_endline s done;;
val func : int -> string -> unit = <fun>
# func 3 "hi";;
hi
hi
hi
- : unit = ()
# let f1 n = func n "curried second param";;
val f1 : int -> unit = <fun>
# f1 4;;
curried second param
curried second param
curried second param
curried second param
- : unit = ()
#