On 22/09/2017 10:23, Marko Rauhamaa wrote:
Bill <bill_nos...@whoknows.net>:
I figure that, internally, an address, a pointer, is being passed by
value to implement pass by reference. Why do you say "they are right"
above? Are you saying it's not pass by reference?
"Pass by reference" could be "pass by reference to object" (Python,
Java, JavaScript, Lisp) or "pass by reference to memory slot" (available
to Pascal and C++).
Memory slots (or lvalues, as they are known in C) are not first class
objects in Python, which makes "pass by reference to memory slot" a bit
tricky in Python. Python *could* add memory slots to its sanctioned
collection of object types, and it *could* add special syntax to express
a memory slot reference and dereference ("&" and "*" in C).
However, Python doesn't need any language changes to implement memory
slots. A memory slot could be defined as any object that implements
"get()" and "set(value)" methods:
I didn't understand your examples.
Can Python be used to write, say, a swap() function that works with any
argument types (not just classes or lists)? Example:
def swap(&a,&b): # made up syntax
a, b = b, a
x=10
y="Z"
swap(x,y)
print (x,y) # "Z" and "10"
If not, then it doesn't have reference passing as it is normally understood.
A simpler example:
def set(&a,value):
a = value
set(x,1000000)
Here the type of x is irrelevant anyway. It doesn't even need to be
initialised to anything first (that might violate something in Python, I
don't know what).
--
bartc
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