The question was (see the original post),  why does a command work in a terminal but not in a method. And, as you know, the answer lies in the scoping. I would say, he (@David Hockenbroch) tries to learn and understand the nature of indirection and is not working on a production grade problem.

But maybe I'm wrong... who knows.

He (@David Hockenbroch) is playing with inderection, using $classmethod() instead of ##class(classname).methodname(...)  does not solve the scoping problem:

ClassMethod testvalidator(class As %String, value As %String) As %Status
{  
  set validator = "sc = $classmethod(class, ""IsValid"", value)"
   write validator,!
   set @validator
   write sc,!
   quit sc
}

The above method gives you the same <UNDEF> error because of non global scoping! By using indirection both variables (validator and sc) must have global scope.

As @Sergei.Shutov pointed out, you can switch off the procdere block by a keyword for the whole class. Additionaly, you can switch on or off the procedure block keyword for a particular  method too. In your case:

class Some.Class  Extends %RegisteredObject
{
/// a procedure block method
ClassMethod ProcBlock()
{
}

/// a nonprocedurblock method
ClassMethod NoProcBlock() [ ProcedureBlock = 0 ]
{
// Caution: All variables have a global scope, hence, they will overwrite variables with the same name, which were created previously. To avoid this, use the NEW command, to protect them (if desired).
}

}

According to the task, "...You will receive an integer number and you will return a new number..."

set s=9999999999999999999
write s --> 10000000000000000000
write AddWater(s) --> 1  // which is the expected result

The above method works also for cases, where s contains a string of digits

set a="9999999999999999999"
write a  --> 9999999999999999999
set res=AddWater(s)
write res ---> 999...<165 more nines>...999
write $length(s) --> 19
write $length(res) --> 171  // 19 * 9 = 171

So why do you show those devils?

Oh, I see right now, we can save one byte...

ClassMethod AddWater(s)
{
   f i=$l(s):-1:1 s t=$e(s,i),$e(s,i)=10**t-1/9*t
   q $tr(s,0)
}

Check this one...

ClassMethod AddWater(s)
{
   f i=$l(s):-1:1 s t=$e(s,i),$e(s,i)="1E"_t-1/9*t
   q $tr(s,0)
}

%FromJSON is not a class, it's a method of %DynamicObject and is available in IRIS and for Cache  version 2016.2 and later.

I don't know exactly what you mean, maybe you have a example for us?

Something like:

DateFrom: 2021-09-27  DateThru: 2021-09-28
Expected time range:  from ???? thru ????

If you create a class, you can it declare as a hidden class, see

https://docs.intersystems.com/iris20211/csp/docbook/DocBook.UI.Page.cls?...

Class My.Class Extends What.Ever [ Hidden ]
{
}

will be a hidden class.  

For your own classes you can adjust this class keyword as you like but for the system classes - there is no chance, they lie somwhere on ISC servers (and, but this is my very own opinion, not very wise. First, I would like to read the documentation for the version I have installed (and not always the latest version) and second, I would like to read the doc everywhere! For example, I have a 10 hour flight, and want to work. And in case, a server only has a  local LAN access, then you have no docu!).

assuming, the variable jsonStr contains the response from the API, then            
            

write jsonStr ---> {"code":200,"status":"OK","data":...
set object={}.%FromJSON( jsonStr )
write object.data.hijri.date

That's all.

you wrote in your original message, I quote "...But if I add one additional column such as below the query fails:" and now, see above, you talk about "batch term session".

I'm confused.

I'm not sure, if I understand your problem correctly...

but if your problem is the terminal width, then you can change the default terminal width from 80 to 132 (Edit --> Window Size) or simply, you use for example PuTTY. Sometimes my PuTTY starts on the left monitor and goes over to the second monitor, so I can see  long lines in its entirety.

Of course, my loop is a little bit too short ;-(  the correct one is

ClassMethod Merge(obj...) {
   set res=obj(1)
   do res.%Remove("NextCursor")
   for i=2:1:obj {
      for j=0:1:obj(i).OptOuts.%Size()-1 do res.OptOuts.%Push(obj(i).OptOuts.%Get(j))
   }
   quit res
}

 Sorry, it seems, a telephone call and writing  does not go together.

If I understand you correctly, all you have to do is a short loop:

ClassMethod Merge(obj...)
{
   set res=obj(1)
   do res.%Remove("NextCursor")
   for i=2:1:obj do res.OptOuts.%Push(obj(i).OptOuts)
   quit res
}

do Merge(json1, json2, json3, ...)

Sorry to say, but your comparsion has some sore points:

a) The very first mistake is, you are comparing programing languages!
This is a disputable attempt because each programing language was created with a specific aim (i.e. use case) in mind. So there are very few languages which can be compared to each other. ObjecStript was created as an Operating-System-and-Database-and-Programing-Language. Nowdays, it's a Database-and-Programming-Language. Python is just a programming language! 

b) The second mistake is, comparing methods with the same name (one may think, they do the same thing) but they have different internal behaviour.

Your Python code reads one line from the file (i.e. characters until the next LF):   
  

line = file.readline()

but your ObjecScript code:

set strBuffer = FileReader.ReadLine(.len, .tSC, .eol)

reads a chunk of data from a stream and tries to extract a line from this chunk (take a look at the source code!). Here you loose (probably) most of the time. 
   
The more comparable statement should have been:

read strBuffer

assuming, the file was opened as   

open filename:"R":0

c) Apart from OS, CPU and Disk (HDD, SSD), where there is no information, did you made both runs under the same buffer state (cold or warm)?

In my opinion you're comparing apples with oranges.