A question on modification of a list via a function invocation

[Rustom Mody]

On Monday, September 4, 2017 at 3:35:54 PM UTC+5:30, Antoon Pardon wrote:
> Op 04-09-17 om 00:44 schreef Dennis Lee Bieber:
> > 	And is a limited theoretical study, heavy in mathematics and light in
> > implementation.
> >
> > 	Programming Languages: Design and Implementation (Terrence W Pratt,
> > 1975, Prentice-Hall) has a whole section (6-9 Subprograms with Parameters:
> > Parameter Transmission Techniques)... 
> >
> > """
> > Basic parameter Transmission Techniques
> >
> > Transmission by Value:  ... the actual parameter is evaluated at the point
> > of call. The /values/ of the actual parameter is then transmitted to the
> > subprogram and becomes the initial value associated with the corresponding
> > formal parameter. ...
> >
> > Transmission by Reference (Location or Simple Name): In transmission by
> > reference a pointer is transmitted, usually a pointer to a data location
> > containing the value. ... Any assignment to Y in SUB will change the value
> > of X back in the calling program.
> 
> IMO that depends on the semantics of the assignment statement. In an environment
> where an assignment copies the value into the object the variable points to, this
> is correct. However if assignment provides a new object that is now bound to the
> variable, it is incorrect.
> 
> The diagram below tries to illustrate the two different assignment semantics:
> 
> BEFORE
>                          +-----+       +-----+
>                          |     |       |     |
>                          |  5  |       |  7  |
>                          |     |       |     |
>                          +-----+       +-----+
> 
>                             ^             ^
>                             |             |
>                            <x>           <y>
> 
> 
>                                  x = y
> AFTER
> 
>             C style                |         Python style
>                                    |
>      +-----+       +-----+         |                  +-----+
>      |     |       |     |         |                  |     |
>      |  7  |       |  7  |         |                  |  7  |
>      |     |       |     |         |            --->  |     |
>      +-----+       +-----+         |           /      +-----+
>                                               /
>         ^             ^                      /           ^
>         |             |                     /            |
>        <x>           <y>                  <x>           <y>

That's fine as far as it goes
But then you have people (Steven above) who feel that python passing has
no exceptions (in parameter passing)
Does a poor job AFAIAC of explaining the difference between foo and bar in foll

>>> def foo(x): x += 2
>>> def bar(x): x.append(2)
>>> a=10
>>> b=[10]
>>> foo(a)
>>> a
10
>>> bar(b)
>>> b
[10, 2]
>>>