Pass by reference or by value?

[Thomas Jollans]

On Thursday 16 August 2007, Robert Dailey wrote:
> Hi,
>
> I previously created a topic named "Pass by reference or by value" where I
> inquired on how python's function parameters work. I received a lot of nice
> responses, however I'm still confused on the topic. Note that I come from a
> C++ background to Python, so any comparisons to C++ would be very helpful.

Very short answer:

Think of normal objects as always-pointers. There are no references. param = 5 
sets the local variable "param" (be that of imaginary type int* or int, I 
don't care) to whatever 5 is. This does not call an operator=, this plain 
overwrites the variable.

If you want to change arguments in that way, you can use a list as an ugly 
hack:

def foo(param):
	param[0] = 5
	print param[0]

a = [4]

foo(a)

yeah, I said ugly. That hack makes sure that a method of the passed object is 
called instead of of the local namespace dict. (please note that I'm throwing 
around abstract concepts without caring about an implementation).

-- 
      Regards,                       Thomas Jollans
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