Some additional picky details:
The unary + operator is a numeric operator so it converts its operand to a number. If a string operand starts with a fractional number then unary + produces a fractional number (in its canonical numeric form) and it throws away any unneeded characters. If you want your numeric result to be an integer then you need to throw away the fractional digits by doing an integer-division by 1. Since the integer-division operator, \, is a numeric operator it always converts its operands to numbers so you no longer need the unary + to do the conversion of a string to numeric representation. E.g.s:
USER>w "0012.543000abc"
0012.543000abc
USER>w +"0012.543000abc"
12.543
USER>w +"0012.543000abc"\1
12
USER>w "0012.543000abc"\1
12
The third argument to %GetNext is not a string value. It is a variable passed by reference: iterator.%GetNext(.key,.value,.type). When this returns then the variable type will contain a string value like “string”, “number”,”object”, etc. If type contains “string” and $isobject(value) is true then value is a %Stream object containing your long string.
Most of the ObjectScript examples above (but not the Python example) take O(n**2) time (i.e., quadratic time) where 'n' is number of values in X. This happens because the $PIECE(X,",",i) starts searching from the beginning of the string or because shortening the string X with
set x=$p(x,",",2,*)
will copy the string 'x' multiple times with the first element deleted before each copy.
The ObjectScript example from Timo Lindenschmid using $LISTNEXT takes O(n) time (linear time). This can be important if $L(X,",") is 1000 or more because such a list with 1000 elements will require about 500,000 scans of "," characters or about 500,000 copies of string characters.
Rich Taylor's Python example should also take linear time.
Another solution would be to build a %DynamicArray object and then iterate through its contents.
Finally, you could build a multi-dim ObjectScript array and iterate through the subscripts with $ORDER. This is method closest to using standard MUMPS/ANSI M/ObjectScript features.