# Python Memory Management

Memory management in Python involves a private heap containing all Python objects and data structures. The management of this private heap is ensured internally by the *Python memory manager*.

## The Private Heap

The private heap is where all Python objects and data structures are stored. The programmer does not have access to this heap directly; instead, the Python memory manager handles it.

## Python Memory Manager

The Python memory manager has different components which deal with various dynamic storage management aspects, like sharing, segmentation, preallocation or caching.

### Hierarchy

1.  **Raw Memory Allocator**: Interacts with the memory manager of the operating system.
2.  **Object-Specific Allocators**: Operates on the same heap and implements distinct memory management policies adapted to the peculiarities of every object type.

## Reference Counting

Python uses reference counting as its primary memory management mechanism.

*   Every object has a reference count.
*   The count increases when an object is referenced (e.g., assigned to a variable).
*   The count decreases when a reference is deleted or goes out of scope.
*   When the count reaches zero, the memory is deallocated.

```python
import sys

a = []
b = a
# The reference count is higher than expected because getrefcount() creates a temporary reference
print(sys.getrefcount(a)) 
```

## Garbage Collection

While reference counting handles most cases, it cannot handle reference cycles (e.g., object A references B, and B references A). Python has a cyclic garbage collector to detect and clean up these cycles.

See [[programming/python/garbage-collection]] for more details.

## Memory Pools (pymalloc)

Python has a specialized allocator for small objects (less than 512 bytes) called `pymalloc`. It uses memory pools to reduce fragmentation and improve performance.

*   **Blocks**: The smallest unit of allocation.
*   **Pools**: A collection of blocks of the same size class.
*   **Arenas**: A collection of pools (typically 256KB chunks).

[[programming/python/python]]