Pass by reference ?

Greg Ewing greg at cosc.canterbury.ac.nz
Wed Apr 5 05:20:35 CEST 2000


Nick Maclaren wrote:
> 
> Unless I am thoroughly confused, Python uses bog-standard call by
> reference, with the wrinkle that assignment is a rebinding rather
> than a copying operation.  AM I confused about that?

The trouble with describing Python parameter passing as
"call by reference" is that that term implies something
like a Pascal VAR parameter, which Python most certainly
does *not* have. That's why Mr. Generowicz got confused -
he thought it meant that a reference to the *variable*
x was being passed.

If I had to pick one of the standard terms, I would describe 
Python parameter passing as call-by-value, with the wrinkle 
that the value being passed is always a reference to an object.

But I think it's better to avoid using any of the terms
developed for describing parameter passing in Algol-like
languages when explaining Python to a newcomer, because
none of them really fit properly, and further explanation
is needed to avoid confusion. It's better to just give the
full explanation in the first place.

-- 
Greg Ewing, Computer Science Dept,
+--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg at cosc.canterbury.ac.nz	   +--------------------------------------+



More information about the Python-list mailing list