Variables versus name bindings [Re: A certainl part of an if() structure never gets executed.]

[88888 Dihedral]

Michael Torrie於 2013年6月20日星期四UTC+8下午2時01分11秒寫道：
> 
>  But since the LISP never really got a form beyond S-expressions,
> 
> leaving us with lots of parenthesis everywhere, Python wins much as the
> 
> Hitchhiker's Guide to the Galaxy wins.

Yep, a list is mutable even it's empty.
But constant integers, floats, strings, and None is immutable.

The  variables in a function of python with default 
parameters which could be mutable or immutable.

def fun1( x, alist=[]):
    alist.append(x*x)
    return alist   ## valid

def fun2(x, alist=None):
    if alist==None: alist=[]
    alist.append(x*x)    
    return alist

# kind of boring to show the name binding mechanism of objects
# in Python in different usages