Use this tag for questions related with argument unpacking, a technique that allows Arrays and Traversable objects to be extracted/unpacked into argument lists/sequences.
argument-unpacking is usually found in PHP, Python and Go.
Questions tagged [argument-unpacking]
144 questions
16
votes
3 answers
Difference call function with asterisk parameter and without
I know what the meaning of an asterisk is in a function definition in Python.
I often, though, see asterisks for calls to functions with parameters like:
def foo(*args, **kwargs):
first_func(args, kwargs)
second_func(*args, **kwargs)
What…
Robert Moon
- 1,025
- 10
- 17
9
votes
1 answer
Auto-unpacking a pair of iterators
In C++, if a function returns a std::pair, we can auto-receive it as follows:
auto pr = some_function();
std::cout << pr.first << ' ' << pr.second;
Now, C++17 standard provides a beautiful way of unpacking this pair directly into separate…
MrProgrammer
- 443
- 3
- 13
8
votes
1 answer
Python - value unpacking order in method parameters
def fun(a, b, c, d):
print('a:', a, 'b:', b, 'c:', c, 'd:', d)
why this one works
fun(3, 7, d=10, *(23,))
and prints out:
a: 3 b: 7 c: 23 d: 10
while this
fun(3, 7, c=10, *(23,))
does not
Traceback (most recent call last):
File…
Łukasz
- 1,980
- 6
- 32
- 52
8
votes
1 answer
How to overload * argument unpacking operator?
I have data like data = [[t1, t2, ...], [v1, v2, ...]]. I want to wrap this in a class so I can call data.t instead of having to use data[0].
I tried to do this with the following:
class Variable:
def __init__(self, data):
self.t =…
pingul
- 3,351
- 3
- 25
- 43
7
votes
2 answers
Packing values into a tuple using *, just like function argument packing
Consider a function defined as:
def fun(a, *args):
print(type(args), args)
When called, it packs the extra positional arguments as a tuple.
>>> fun(2, 3, 4)
(3, 4)
I want to achieve a similar thing outside of function…
2020
- 2,821
- 2
- 23
- 40
6
votes
2 answers
MATLAB: Accessing an element of a multidimensional array with a list
I have a d-dimensional array, A, and vector inds with length equal to d. I would like to access the value of A at inds.
Ideally, I'd do something like A(*inds) (borrowing the unpacking syntax from Python). I'm not sure how to do this in MATLAB.
If…
emchristiansen
- 3,550
- 3
- 26
- 40
6
votes
3 answers
How to ignore unpacked parts of a tuple as argument of a lambda?
In Python, by convention, the underscore (_) is often used to throw away parts of an unpacked tuple, like so
>>> tup = (1,2,3)
>>> meaningfulVariableName,_,_ = tup
>>> meaningfulVariableName
1
I'm trying to do the same for a tuple argument of a…
Julian
- 4,170
- 4
- 20
- 27
6
votes
1 answer
Unpacking a dictionary and passing to a function as keyword parameters
I am trying in python to unpack some dict into some function:
I have a function that get packet as parameter (that should be dict)
def queue(self, packet):
self.topic.publish(self.message, self.client, **packet)
and I call it this way:
queue({
…
ET-CS
- 6,334
- 5
- 43
- 73
5
votes
4 answers
Syntax error when passing unpacked argument to print in Python
Instead of a simple debug/log print as this:
print "error ", error_number
I would like to use a log function that I can expand when required looking something like this:
def log(condition, *message):
if():
…
hobb
- 166
- 1
- 10
5
votes
3 answers
Unpack variadic template to initializer_list and call two functions at once
I have two vectors:
std::vector v1{ 1, 2, 3 };
std::vector v2{ 4, 5, 6 };
I want to create an object of std::initializer_list which holds iterators to the first and last elements of above vectors.
I want to have a function with a variadic…
Ragdoll Car
- 141
- 6
5
votes
3 answers
Unpack nested list for arguments to map()
I'm sure there's a way of doing this, but I haven't been able to find it. Say I have:
foo = [
[1, 2],
[3, 4],
[5, 6]
]
def add(num1, num2):
return num1 + num2
Then how can I use map(add, foo) such that it passes num1=1, num2=2 for…
binaryfunt
- 6,401
- 5
- 37
- 59
5
votes
2 answers
Unpacking Parameter Pack in C++
I have two functions f and g. f calculates it's return value asynchronously and returns a future. Now, based on several return values of f, I want to call g, but I want to make sure that the computations of the values of f happen in…
ssb
- 7,422
- 10
- 36
- 61
4
votes
2 answers
Understanding the asterisk operator in python when it's before the function in a parenthesis
I know that the asterisk is used to unpack values like system args or when you unpack lists into variables.
But I have not seen this syntax here before in this example of asyncio.
I was reading this article here,…
anarchy
- 3,709
- 2
- 16
- 48
4
votes
6 answers
Why does max(*list) and max(list) do the same thing in python?
See below example:
>>>f = [[1],[2],[3]]
>>>max(f)
Out[21]: [3]
>>>max(*f)
Out[22]: [3]
The unpack operator did not have an effect here, I am trying to unpack a list and get a maximal value of matrix(two dim list).
Pythoner
- 5,265
- 5
- 33
- 49
4
votes
2 answers
How does ruby unpack arguments passed into Proc?
a_proc = Proc.new {|a,b,*c| p c; c.collect {|i| i*b }}
puts a_proc[2,2,4,3]
Code above is pretty intuitive according to https://ruby-doc.org/core-2.2.0/Proc.html, a_proc[2,2,4,3] is just a syntax sugar for a_proc.call(2,2,4,3) to hide “call”
But…
Ze Gao
- 91
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