Call by reference and address in Python

[psbasha]

Hi,

Is Python supports Call by reference and Call by address in function or methods,without using C/C++ modules?.

Thanks in advacne
PSB

[bartonc]

Hi,

Is Python supports Call by reference and Call by address in function or methods,without using C/C++ modules?.

Thanks in advacne
PSB

Almost everything in python is pass by reference. If you:

def SomeFunction(listTypeArg):
    listTypeArg[0] = 1

aList = [0, 0, 0]

SomeFunction(alist)
print aList

You get:
[1, 0, 0]

You can not, however, get the address of aList as you can in C. The beauty of python is that we never worry about where a variable is or what it's lifespan is. It's all taken care of.

[Motoma]

You can not, however, get the address of aList as you can in C. The beauty of python is that we never worry about where a variable is or what it's lifespan is. It's all taken care of.

Beauty, or HACKER'S NIGHTMARE?!

I'll leave you to ponder.

[cybervegan]

Beauty, or HACKER'S NIGHTMARE?!

I'll leave you to ponder.

It's a beauty, because it means that it's far less likely that you get any of the following by writing valid python code:

1) memory leaks (where memory is not deallocated when no longer needed -this doesn't include memory leaks from C/C++ modules)
2) double-frees (freeing an already free'd memory block)
3) dangling pointers (pointers that point to deallocated memory)
4) orphaned memory (memory allocated, but with no pointers amed at it)
5) mangled pointers (pointers that point to the wrong bit of memory)

and probably some more too.

If a program *needs* to access memory and pointers directly, it's the wrong problem domain for python. The only memory management problem I can think of that python exhibits (and then only by bad design) is cyclic references, where A refers to B which refers to A. Without care, deleting (and thus reclaiming the memory of) A or B is potentially problematic - you have to remember to break the reference to A from B before destroying A.

It all comes down to choosing the right tool for the job.

:-D cybervegan

[bartonc]

It's a beauty, because it means that it's far less likely that you get any of the following by writing valid python code:

1) memory leaks (where memory is not deallocated when no longer needed -this doesn't include memory leaks from C/C++ modules)
2) double-frees (freeing an already free'd memory block)
3) dangling pointers (pointers that point to deallocated memory)
4) orphaned memory (memory allocated, but with no pointers amed at it)
5) mangled pointers (pointers that point to the wrong bit of memory)

and probably some more too.

If a program *needs* to access memory and pointers directly, it's the wrong problem domain for python. The only memory management problem I can think of that python exhibits (and then only by bad design) is cyclic references, where A refers to B which refers to A. Without care, deleting (and thus reclaiming the memory of) A or B is potentially problematic - you have to remember to break the reference to A from B before destroying A.

It all comes down to choosing the right tool for the job.

:-D cybervegan

I so agree. Thanks for the input.

[Motoma]

I so agree. Thanks for the input.

Only a FOOL would see these as good points!

[psbasha]

Only a FOOL would see these as good points!

>>> def f(l):
	list[0]=2

	
>>> a=[0,0,0]
>>> f(a)
>>> print a
[0, 0, 0]
>>>

I am not able to get the output as suggested in the discussion.Coul d anybody help me in solving this or umderstanding this problem

[Motoma]

>>> def f(l):
list[0]=2


>>> a=[0,0,0]
>>> f(a)
>>> print a
[0, 0, 0]
>>>

I am not able to get the output as suggested in the discussion.Coul d anybody help me in solving this or umderstanding this problem

Well, what you did here, was you passed a list as l, and then you set the value of list (not l) to 2.

>>> def f(l):
	l[0] = 2

>>> a = [0, 0, 0]
>>> f(a)
>>> a
[2, 0, 0]

[bartonc]

>>> def f(l):
	list[0]=2

	
>>> a=[0,0,0]
>>> f(a)
>>> print a
[0, 0, 0]
>>>

I am not able to get the output as suggested in the discussion.Coul d anybody help me in solving this or umderstanding this problem

You are making progress now! You have posted some code. This is what we are good at helping with here.

>>> def f(l):
	# list[0]=2 # you need to use I, to assign to Don't use "list" that word is reserved for creating lists.

	I[0]=2

	
>>> a=[0,0,0]
>>> f(a)
>>> print a
[0, 0, 0]
>>>

[psbasha]

You are making progress now! You have posted some code. This is what we are good at helping with here.

>>> def f(l):
	# list[0]=2 # you need to use I, to assign to Don't use "list" that word is reserved for creating lists.

	I[0]=2

	
>>> a=[0,0,0]
>>> f(a)
>>> print a
[0, 0, 0]
>>>

It is working fine

Thanks
PSB

[bartonc]

It is working fine

Thanks
PSB

You are welcome.