CODEWITHSUNDEEP
pythonmemory-address
Shanu
Shanu

Reputation: 1

python;address of variable,integer values are immutable?

I read somewhere that in python id() function gives the address of object being pointed to by variable.for eg; x =5, id(a) will give the address of object 5 and not the address of variable x.then how can we know the address of variable x??

Upvotes: 0

Views: 46

Answers (2)

Tony Suffolk 66
Tony Suffolk 66

Reputation: 9704

Firstly - the id() function doesn't officially return the address, it returns a unique object identifier which is guaranteed to be unique for the life time of that object. It just so happens that CPython uses the address for that unique id, but it could change that definition at any time. It is of no use anyway knowing what the id() actually means - there is nothing in Python that allows objects to be accessed via their id.

You asked about the address of the variable, but in Python, variables don't have an address. I know in languages like C, C++ etc, a named variable is simply a named location in memory into which a data item is stored.

In Python though - and certainly in CPython, variables aren't a fixed location in memory. In Python all variables simply exist as a key in a dictionary that is maintained as your code runs.

When you say 

x = 5

in python, it finds the int(5) object and then builds a key value pair in the local scope dictionary. in a very real terms this equivalent to : 

   __dict__['x'] = 5

or something similar depending on the scope rules.

So there will be an address somewhere in memory which holds the string 'x', but that isn't the address of the variable at all.

Upvotes: 1

lucidbrot
lucidbrot

Reputation: 6156

The python3 documentation says

id(object)
Return the “identity” of an object. This is an integer which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same id() value.

CPython implementation detail: This is the address of the object in memory.

So this is not guaranteed to be the address. (What did you want to do with the address?)
In CPython it just happens to be the address, because the address of an object is unique apparently and so it is an easy choice.

Generally, Python does not use pointers in the same way as C does. I recommend you to instead search for how whatever you'd like to do is generally done in python. Changing the way you think about the task is likely a more frictionless way than imposing C mentality onto Python.

Upvotes: 0

Related Questions