How many bytes per element are there in a Python list (tuple)?

Question

For example, how much memory is required to store a list of one million (32-bit) integers?

alist = range(1000000) # or list(range(1000000)) in Python 3.0
         


        

Answer 1

Addressing "tuple" part of the question

Declaration of CPython's PyTuple in a typical build configuration boils down to this:

struct PyTuple {
  size_t refcount; // tuple's reference count
  typeobject *type; // tuple type object
  size_t n_items; // number of items in tuple
  PyObject *items[1]; // contains space for n_items elements
};

Size of PyTuple instance is fixed during it's construction and cannot be changed afterwards. The number of bytes occupied by PyTuple can be calculated as

sizeof(size_t) x 2 + sizeof(void*) x (n_items + 1).

This gives shallow size of tuple. To get full size you also need to add total number of bytes consumed by object graph rooted in PyTuple::items[] array.

It's worth noting that tuple construction routines make sure that only single instance of empty tuple is ever created (singleton).

References: Python.h, object.h, tupleobject.h, tupleobject.c