Scope

you can watch parallel the video for C/C++ (german): https://www.youtube.com/watch?v=JDDWSWef0ng&list=PLEWVM-KBUSpmWSfyoFdD_hLWAY_9tTgi5&index=12

The scopes are implemented with a stack implemented with the CPU. https://de.wikipedia.org/wiki/Stapelspeicher#/media/Datei:ProgramCallStack2_en.svg

import ROOT

C++

%%cpp
#include <iostream>
using namespace std;
int g=40;
//int main(int argc,char *argv[])
{                    
    cout <<"in main before local variable definition: "<<g<<endl;
    int g=42;             //the local scope does not overrides the global scope
    cout <<"in main after local variable definition: "<<g<<endl;
    {
        cout <<"in subscope before local variable: "<<g<<endl;
        int g=43;
        cout <<"in subscope after local variable: "<<g<<endl;
    }
    cout<<"in main after subscope: "<<g<<endl;                
}

in main before local variable definition: 40
in main after local variable definition: 42
in subscope before local variable: 42
in subscope after local variable: 43
in main after subscope: 42

C

%%cpp
#include <stdio.h>

int g=40;
//int main(int argc,char *argv[])
{                    
    //printf("in main before local variable definition: %d\n",g);     //this is not allowed in c, the definitions must come first
    int g=42;             //the local scope does not overrides the global scope
    printf("in main after local variable definition: %d\n",g);  //this is not allowed in c
    {
        //printf("in subscope before local variable: %d\n",g);  //this is not allowed in c
        int g=43;
        printf("in subscope after local variable: %d\n",g);
    }
    printf("in main after subscope: %d\n",g);
}

in main after local variable definition: 42
in subscope after local variable: 43
in main after subscope: 42

Javascript

javascript also has local scope as in c if defined with let

%%js //the next line is only necessary in jupyter notebooks
element.setAttribute('style', 'white-space: pre;');console.log=function(text){element.textContent+=text+"\n"}

let g=40
{
    console.log(g)
    g=41
    console.log(g)
}

console.log(g)

%%js //the next line is only necessary in jupyter notebooks
element.setAttribute('style', 'white-space: pre;');console.log=function(text){element.textContent+=text+"\n"}

let g=40
{
    //console.log(g) //not allowed
    let g=41
    {
        let g=42;
        console.log(g);
    }
    console.log(g)
}


console.log(g)

%%js //the next line is only necessary in jupyter notebooks
element.setAttribute('style', 'white-space: pre;');console.log=function(text){element.textContent+=text+"\n"}


{
    //console.log(g) //not allowed
    var g=41 //defines a global variable but not when used inside a function!
    {
        let g=42;
        console.log(g);
    }
    console.log(g)
}


console.log(g)

%%js //the next line is only necessary in jupyter notebooks
element.setAttribute('style', 'white-space: pre;');console.log=function(text){element.textContent+=text+"\n"}

//Variables declared with var, let and const are quite similar when declared inside a function.
let g=40;

function test(){
    var g=42;
    {
        //console.log(g); //not allowed
        let g=43;
        console.log(g);
    }
    console.log(g)
}

test()
console.log(g)

Python

Python only knows three scopes: global, local and class. In python scopes are defined by indentation. It is important to keep a consistent indentation. We need to use functions to show the scopes.

g=40
def myfunc():
  g = 42
  def myinnerfunc():
    print(g)
  myinnerfunc()
  print(g)

myfunc()
print(g)

42
42
40

g=40
def myfunc():
  g = 42
  def myinnerfunc():
    g=43
    print(g)
  myinnerfunc()
  print(g)

myfunc()
print(g)

43
42
40

def myfunc():
  g = 42
  def myinnerfunc():
    print(g)  #not allowed
    g=43
    print(g)
  myinnerfunc()
  print(g)

myfunc()

---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
Cell In[11], line 10
      7   myinnerfunc()
      8   print(g)
---> 10 myfunc()

Cell In[11], line 7, in myfunc()
      5   g=43
      6   print(g)
----> 7 myinnerfunc()
      8 print(g)

Cell In[11], line 4, in myfunc.<locals>.myinnerfunc()
      3 def myinnerfunc():
----> 4   print(g)  #not allowed
      5   g=43
      6   print(g)

UnboundLocalError: cannot access local variable 'g' where it is not associated with a value

g=40
def myfunc():
  g = 42
  def myinnerfunc():
    global g #this is accessing the global g
    g=43
    print(g)
  myinnerfunc()
  print(g)

myfunc()
print(g)

43
42
43

Fortran

Fotran does only have function scopes