[Tutor] Doubt

[Peter Otten]

Amit Yadav wrote:

> How can simply typing
> 
>  print "hello world"
> 
> work?
> Like without including any header file or import statements how can it
> work.

In Python 2 print is part of the syntax that the compiler knows, just like 

int

or

for (... ) {}

in C. In Python 3 print is just a name, like len, say, in both py2 and py3.
A name on the module level is looked up first in the module's namespace, and 
if it's not found in another special namespace that is built into the 
interpreter:

>>> __builtins__
<module '__builtin__' (built-in)>
>>> __builtins__.len is len
True

The unqualified name "len" is the same object as __builtins__.len because it 
is looked up there. When you overwrite it with your own name this will take 
precedence:

>>> def len(x): return 42
... 
>>> __builtins__.len is len
False
>>> len("abc")
42

OK that was probably a bad idea, let's remove our len() to see the built-in 
again:

>>> del len
>>> len("abc")
3

The built-in namespace is user-writeable:

>>> __builtins__.spam = "ham"
>>> spam
'ham'