* [related file](#related-file)

* [memory layout](#memory-layout)

* [how element stored inside](#how-element-stored-inside)

* [free list](#free-list)

* cpython/Include/cpython/tupleobject.c

* cpython/Include/tupleobject.h

* cpython/Objects/tupleobject.c


The structure of **tuple** object is more simple than other python object.

Obviously, **ob_item** is an array of PyObject* pointer, all elements will be stored inside the **ob_item** array, But how exactly each element stored in **PyTupleObject**? Is the first element begin at the 0 index? What is the resize strategy?

Let's see

```python3

t = tuple()

```


```python3

t = ("aa", )

```


```python3

t = ("aa", "bb", "cc", "dd")

```

**ob_size** represents the size of **PyTupleObject** object, because tuple object is immutable, the **ob_item** is the start address of an array of pointer to **PyObject**, and the size of this array is **ob_size**, there's no need for resize operation.


The free_list mechanism used here is more interesting than [free_list in list](https://github.com/zpoint/CPython-Internals/blob/master/BasicObject/list/list.md#delete-and-free-list)

```c

static PyTupleObject *free_list[PyTuple_MAXSAVESIZE];

static int numfree[PyTuple_MAXSAVESIZE];

```

let's exam what **free_list** and **numfree** is

we assume that python interpreter don't create/deallocate any tuple object internally during the following code

```python3

>>> t = tuple()

>>> id(t)

>>> del t

>>> t = tuple()

>>> id(t) # same as previous deleted one

>>> t2 = tuple()

>>> id(t2) # same as t

```


```python3

>>> t = ("aa", )

>>> id(t)

>>> del t

>>> t = ("bb", )

>>> id(t) # it's not repeatable, because I assume that python intepreter don't create/deallocate any tuple object during execution

>>> t2 = ("cc", )

>>> del t

>>> del t2

```


num_free[i] means how many objects left in free_list[i], when you create a new tuple with size i, cpython will use the top object at free_list[i]

```python3

>>> t = ("aa", )

```


```python3

>>> t2 = ("aa", "bb")

>>> t3 = ("cc", "dd")

>>> t4 = ("ee", "ff")

>>> t5 = ("gg", "hh")

>>> del t2

>>> del t3

>>> del t4

>>> del t5

```