How are variables stored in python - Stack or Heap? | Python | Prepbytes (2023)

Last Updated on June 23, 2022 by Ria Pathak

How are variables stored in python - Stack or Heap? | Python | Prepbytes (1)

Memory allocation is the process of allocating memory to a computer program. In Python, the process of memory allocation and deallocation is handled automatically as there is a garbage collector which is created in python so that users don’t have to handle the process of garbage collection.

Garbage Collection

It is a process in which memory is deallocated when it is not in use to make the space available for other objects. In case, when no one is referencing the object in memory then in the virtual machine, the garbage collector comes to work to automatically delete the object in the heap memory.

Reference Counting

It is a procedure that works by counting the number of times an object is referenced by other objects in the computer. This count for an object is decremented when reference to an object is removed. And when this count becomes zero, then that object is deallocated.
For example, in the case of two variables having the same value. Then the virtual machine instead of making two different objects, it makes two pointers pointing at the same object created in the private heap.


  • Python
b = 3a = 6b = 6print(id(a) == id(b))

Output: True

Memory allocation in Python

There are two parts of memory:

  • Stack memory
  • Heap memory

The function calls and the references are stored in the stack memory whereas all the value objects are stored in the heap memory.

Work of Stack Memory

It is called stack memory allocation as the allocation happens in the function call stack. At the time of allocation, the memory size is known to the compiler and when there is a function call that happens, then its variable gets memory allocated on the stack.
It is the memory that is needed inside a particular function. When the function is called, it will be added to the program call’s stack. Variable initialization inside the function is temporarily stored in the function call stack, where it will be deleted after the completion of the function. This memory allocation onto a contiguous memory is handled by the compiler, developers do not have to worry about it.


  • Python
def func(): a = 10 b = "" c = {}

Work of Heap Memory

Heap memory allocation is done when memory is allocated at the time of execution of a program written by the programmer. As there is a pile of memory space available in the process of allocation and de – allocation, that’s why it is known as heap memory. The variable which is required globally in the program is stored in heap memory.


  • Python
# This memory for 5 integers is allocated in the heap.arr = [0] * 5

This article tried to discuss How are variables stored in python – Stack or Heap?. Hope this blog helps you understand the concept. To practice more problems feel free to check MYCODE | Competitive Programming at Prepbytes.


How are variables stored in python - Stack or Heap? | Python | Prepbytes? ›

Whenever we create variables of non-primitive data types( for example lista, custom objects pr dictionaries), the variable itself(reference) is stored on the stack, while on the other hand the object's data is stored on the heap memory.

Are variables stored in stack or heap? ›

Local variables (i.e. those that are declared inside methods) are stored on the stack. This means their values are stored on the stack, therefore meaning that local reference type variables have references stored on the stack and local value type variables have actual values stored on the stack.

Does Python have heap and stack memory? ›

When we create an object 14, it stores in heap memory (as discussed before), and its reference is stored in stack memory. Same for the object “Python”.

How are variables stored in heap? ›

The short answer is that “automatic” variables are stored on the stack and the “dynamic” ones on the heap. Automatic variables are the ones declared in a function or procedure and created when it begins and they are deleted when it ends (returns). The dynamic variables are stored in an area of memory called the heap.

How is data stored in Python? ›

Python Data Persistence - Introduction

Data so received, is stored in computer's main memory (RAM) in the form of various data structures such as, variables and objects until the application is running. Thereafter, memory contents from RAM are erased.

How are variables stored in a stack frame? ›

The stack is used for dynamic memory allocation, and local variables are stored at the top of the stack in a stack frame. A frame pointer is used to refer to local variables in the stack frame. Figure 110: Stack frame before and after the LINK instruction.

Are variables stored on stack or heap in C#? ›

Usage: The stack is generally used for storing small, short-lived variables such as local variables and function parameters, while the heap is generally used for storing larger, longer-lived objects.

How does Python store variables? ›

All objects and instance variables are stored in the heap memory. When a variable is created in Python, it is stored in a private heap which will then allow for allocation and deallocation. The heap memory enables these variables to be accessed globally by all your program's methods.

Is Python heap based? ›

Python uses the heap data structure as it is a highly efficient method of storing a collection of ordered elements. It is useful for keeping track of the largest and smallest elements in a collection, which is a common task in many algorithms and data structures.

Does Python use a stack? ›

Python's built-in data structure list can be used as a stack. Instead of push(), append() is used to add elements to the top of the stack while pop() removes the element in LIFO order. Unfortunately, the list has a few shortcomings. The biggest issue is that it can run into speed issues as it grows.

Are Python variables in heap? ›

As there is a pile of memory space available in the process of allocation and de – allocation, that's why it is known as heap memory. The variable which is required globally in the program is stored in heap memory. Example: Python.

Does Python store data in memory? ›

Memory management in Python involves the management of a private heap. A private heap is a portion of memory that is exclusive to the Python process. All Python objects and data structures are stored in the private heap. The operating system cannot allocate this piece of memory to another process.

Are final variables stored in heap? ›

final variable also stored in stack but the copy that variable which a inner class have stored in heap. synthetic field are filed which actually doesn't exist in the source code but compiler create those fields in some inner classes to make those field accessible.

How is a Python list stored in memory? ›

The list is based on an array. An array is a set of elements ① of the same size, ② located in memory one after another, without gaps. Since elements are the same size and placed contiguously, it is easy to get an array item by index. All we need is the memory address of the very first element (the "head" of the array).

How to store data in Python class? ›

dataclass module is introduced in Python 3.7 as a utility tool to make structured classes specially for storing data. These classes hold certain properties and functions to deal specifically with the data and its representation. Although the module was introduced in Python3. 7, one can also use it in Python3.

Where does Python allocate memory? ›

The allocation happens on contiguous blocks of memory. We call it stack memory allocation because the allocation happens in the function call stack. The size of memory to be allocated is known to the compiler and whenever a function is called, its variables get memory allocated on the stack.

Are variables in main on the stack? ›

main is just another function. Variables go on the stack unless malloc 'd just like elsewhere.

Where are variables stored? ›

Variables are usually stored in RAM. This is either on the heap (e.g. all global variables will usually go there) or on the stack (all variables declared within a method/function usually go there). Stack and Heap are both RAM, just different locations. Pointers have different rules.

Are variables stored in stack Java? ›

All Local Variables and method calls gets stored in Stack , But Instance variables and Objects reside inside the Heap . We can use -Xms and -Xmx JVM option to define the startup size and maximum size of heap memory.

Are function variables stored in the heap? ›

If they are a reference type, they are stored in the heap and a pointer to the memory location is pushed on the stack. When the function returns, the values are popped back off the stack and eventually the garbage collector will notice the memory on the heap no longer has a pointer to it and will clean it up too.


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