somevar = 100;

      function test()
      {
        somevar = 1;
        return somevar;
        if(false) { var somevar; }
      }

      alert(test());
      alert(somevar);

if(false) { var somevar; }

CS>>      somevar = 100;

CS>>      function test()
CS>>      {
CS>>        somevar = 1;
CS>>        return somevar;
CS>>        if(false) { var somevar; }
CS>>      }

CS>>      alert(test());
CS>>      alert(somevar);
CS>>

somevar = 100;
function test()
{
   if(true)
   {
     somevar = 1;
     return somevar;
   }
   else { var somevar; } // <<<<<
   return 0;
}

nlist = 100

def test():
    nlist = 1
    global nlist
    return nlist

Python 2.6.2 (r262:71600, Jun  6 2009, 22:14:54) 
[GCC 4.4.0 20090526 (prerelease)] on linux2
[code]
и

somevar = 100

def test():
    somevar = 1
    return somevar
    if False:
        global somevar
        pass

print(test())
print(somevar)

1.py:7: SyntaxWarning: name 'somevar' is assigned to before global declaration
  global somevar
1
1

somevar = 100

def test():
    somevar = 1
    return somevar
    if False:
        #global somevar
        pass

print(test())
print(somevar)

1
100

1.py:7: SyntaxWarning: name 'somevar' is assigned to before global declaration
global somevar

CS>      somevar = 100;

CS>      function test()
CS>      {
CS>        somevar = 1;
CS>        return somevar;
CS>        if(false) { var somevar; }
CS>      }

CS>      alert(test());
CS>      alert(somevar);
CS>

somevar = 100;

 function test()
 {
   somevar = 1;
   return somevar;
   (function(){
     if(false) { var somevar; }
   })();
 }

JavaScript: The Good Parts By Douglas Crockford:
...
JavaScript's syntax comes from C. In all other C-like languages, a block (a set of statements wrapped in curly braces) creates a scope. Variables declared in a block are not visible outside of the block. JavaScript uses the block syntax, but does not provide block scope: a variable declared in a block is visible everywhere in the function containing the block. This can be surprising to programmers with experience in other languages.

In most languages, it is generally best to declare variables at the site of first use. That turns out to be a bad practice in JavaScript because it does not have block scope. It is better to declare all variables at the top of each function.

print (-1)
somevar = 100
print (0)
def test():
    print (2)
    somevar = 50
    print (3)
    return somevar
    if False:
        global somevar
        pass

print (1)
print(test())
print (4)
print(somevar)
print (5)

1.py:10: SyntaxWarning: name 'somevar' is assigned to before global declaration
  global somevar
-1
0
1
2
3
50
4
50
5

CS>>nlist = 100

CS>>def test():
CS>>    nlist = 1
CS>>    global nlist
CS>>    return nlist

CS>>

def test():
    nlist = 1
    if true:
      global nlist
      return nlist

Блок не определяет новой области выполнения. Только Программа и ОбъявлениеФункции создают новую область видимости.