passing by refference

[Doug Quale]

Joshua Marshall <joshway_without_spam at myway.com> writes:

> David Abrahams <dave at boost-consulting.com> wrote:
> > Doug Quale <quale1 at charter.net> writes:
> 
> >> If Python is not call-by-value, what is an r-value in Python that
> >> differs from what is passed to a function?
> 
> > I should probably stay out of this, but...
> 
> > it doesn't make a whole lot of sense to talk about r-values and
> > l-values in Python, because those terms are normally defined in terms
> > of assignment:
> 
> >    "an r-value is something that can appear on the right hand side of
> >    an assignment"
> 
> >    "an l-value is something that can appear on the left hand side of
> >    an assignment"
> 
> > In Python, the only things that can appear on the LHS of an assignment
> > are names (not values in any reasonable sense).
> 
> This isn't true.  Expressions like "X", "(A, B)", and "A[i]" can be
> l-values or r-values, depending on the context--whether they're on the
> left side of an assignment or not.  Expressions like "2", "()", and
> "f(1)" can only br r-values (you can't assign to them).
> 
> The terms "l-value" and "r-value" apply to any language which has assignment.

Joshua is correct.  Names are not the only thing that can appear on
the left hand sides of Python assignments and l-value does make sense
in Python.