This content originally appeared on DEV Community and was authored by Siddhesh Agarwal
In this post, I will try to improve your idea about memory in python using the in-built id() function. For those of you who don't know what id() is:
The
id()function returns a unique ID of the object. All objects in python have a unique ID and no 2 different values correspond to the same ID.
So let us begin with a small example:
a = b = 500
print(id(a) == id(b))
Fun fact: In python,
id(a) == id(b)is analogous toa is b.
The above code prints True because python creates the variable b with the value 500 and then creates a variable a pointing to the value of b. This implies that a and b are pointing towards the same memory location and hence the same ID.
Now let us raise the bar:
a = 500
b = 500
print(id(a) == id(b))
The above code prints False because:
- Python creates a variable
apointing to the value500in the memory. - Then it creates another variable
bpointing to another value500(yeah, both 500 are different).
Hence, both have different IDs because both point towards different memory locations.
I hope you guys aren't confused because there is more to come. Guess the output for this:
a = 50
b = 50
print(id(a) == id(b))
You guys may think "This is the previous question with different values. I know the answer is False" but not so fast.
For small integers (The CPython range is -5 to 256, both inclusive), then integer objects (<class 'int'>) are shared. This is done entirely to save space. The memory imprint of the console would be significantly larger if these objects weren’t sharing their memory.
So the correct answer is True
Okay, okay. Just one more to go. The last one:
a = 500
id1 = id(a)
a = 500
id2 = id(a)
print(id1 == id2)
Well, even though I am re-declaring the same variable with the same value, the answer is most likely to be False. I'll explain to you why. When you re-declare a variable in python, the interpreter works in the same way as a declaration. i.e. It entirely deletes the before existing value and creates a variable with the new value. So when we give a = 500, the second time the interpreter deletes the previously existing value of a and create a new memory location for 500 where a would point towards. Both these IDs are most likely to be different.
SO, the answer is False.
NOTE: If the above example had a number belonging to the inclusive range -5 to 256, the answer would have been True. this is because number belonging to the inclusive range have a fixed memory location.
This content originally appeared on DEV Community and was authored by Siddhesh Agarwal
Siddhesh Agarwal | Sciencx (2021-12-18T04:28:59+00:00) id() in python. Retrieved from https://www.scien.cx/2021/12/18/id-in-python/
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