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Unpacking a list from a function gives a list is not defined error


Unpacking a list from a function gives a list is not defined error

By : Akito
Date : November 18 2020, 11:13 AM
seems to work fine , Try this:
code :
# -*- coding: utf-8 -*-
#!/usr/bin/python


import os.path
import re
def request ():
    print ("What file should I write to?")
    file = input ()
    thing = os.path.exists (file)
    # thing is a boolean variable but not a string, no need to use '=='
    if thing:
        start = 0
    elif re.match ("^.+.\txt$", file):
        stuff = open (file, "w")
        stuff.write ("Requests on what to add to the server.")
        stuff.close ()
        start = 0
    else:
        start = 1
    go = "yes"
    list1 = (start, file, go)
    return list1
start = 1
while start == 1:
    # you need to get return value of function request
    list1 = request ()
    (start, file, go) = list1
    # Or you can simply write this way  (start, file, go) = request()


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recursive unpacking of a list through function signatures

recursive unpacking of a list through function signatures


By : user3492364
Date : March 29 2020, 07:55 AM
will help you You cannot do this for the built in list type, as you wouldn't be able to get the types to match up.
For instance, one might think it'd be possible with a function of type 'a list list -> 'a list, and then applying it recursively until it reaches a base case of a non-nested list. You would, however, not be able to detect the base case in any way, leaving your types mismatched.
code :
datatype 'a nestableList = Cons of 'a * 'a nestableList
                         | NCons of 'a nestableList * 'a nestableList
                         | Nil;
(* The list [[1, 2], [[3], [4, 5, 6]]] *)
val nlist = NCons(
              Cons(1, Cons(2, Nil)),
              NCons(
                NCons(
                  Cons(3, Nil),
                  Cons(4, Cons(5, Cons(6, Nil)))
                ),
                Nil
              )
           );
fun flatten nls =
let
  fun flatten_ Nil                 = []
    | flatten_ (NCons(head, tail)) = flatten head @ flatten tail
    | flatten_ ( Cons(head, tail)) = head :: flatten tail
in
    flatten_ nls
end;
val flattenedNlist = flatten nlist;     (* Yields [1, 2, 3, 4, 5, 6] *)
Unpacking more than one list as argument for a function

Unpacking more than one list as argument for a function


By : Patrick Warley
Date : March 29 2020, 07:55 AM
Hope that helps Because, as per the Function call syntax, this is how the argument list is defined
code :
argument_list ::=  positional_arguments ["," keyword_arguments]
                     ["," "*" expression] ["," keyword_arguments]
                     ["," "**" expression]
                   | keyword_arguments ["," "*" expression]
                     ["," keyword_arguments] ["," "**" expression]
                   | "*" expression ["," keyword_arguments] ["," "**" expression]
                   | "**" expression
Flatten a nested list using list unpacking in a list comprehension

Flatten a nested list using list unpacking in a list comprehension


By : Mahesh Ramuni
Date : March 29 2020, 07:55 AM
With these it helps No, I don't believe they've added support for list unpacking inside a comprehension yet.
As an alternative, you can use itertools.chain:
code :
>>> from itertools import chain
>>> list(chain.from_iterable([a, b]))
[1, 2, 3, 4, 5, 6]
>>> [y for x in [a, b] for y in x]
[1, 2, 3, 4, 5, 6]
Unpacking of list in function but not needed when its done with MAP()?

Unpacking of list in function but not needed when its done with MAP()?


By : user3342497
Date : March 29 2020, 07:55 AM
To fix the issue you can do In addition to ksourav's answer,
In the docs you find that map(function, iterable, ...) "Return[s] an iterator that applies function to every item of iterable, yielding the results". As ksourav points out in his answer, the items you pass are strings and thus iterables themselves - so the function just returns the last letter in uppercase, like
code :
s = 'lan'
for char in s:
    print(char.upper())
# L
# A
# N
t = ('lan',)
for element in t:
    print(element.upper())
# LAN
m = list(map(lambda x: x.upper(), lis))
# or even better
m = [s.upper() for s in lis]
C++ - unpacking a #defined list of integers into a

C++ - unpacking a #defined list of integers into a


By : Paranjay Sharma
Date : October 13 2020, 04:00 PM
I wish did fix the issue. I have the following code: , Simply place the macro inside an initializer list.
code :
#include <iostream>
#include <vector>

#define ROTATIONS 135, 270, 0,0 , 315, 135

int main(){
    std::vector<float> rotations_vector = {ROTATIONS};

    for (const auto& r : rotations_vector){
        std::cout << r << ' ';
    }
}
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