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pythonpython-2.7cpython

How python variables look like in memory

I want to know how a Python variable (int, list, tuple) look like in memory. And this is where I am right now. 

from ctypes import string_at
from sys import getsizeof
from binascii import hexlify
string_at(id(a), getsizeof(a))

I expect it will return the hex representation of a variable in the memory.

However, here is the output when I assign value 1,2,3 to variable 'a':

1 - '\xd6\x05\x00\x00\x00\x00\x00\x00\xc0\x92\x17\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00'
2 - '\x17\x02\x00\x00\x00\x00\x00\x00\xc0\x92\x17\x00\x01\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00'
3 - '\xdc\x00\x00\x00\x00\x00\x00\x00\xc0\x92\x17\x00\x01\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00'
4 - '\x06\x01\x00\x00\x00\x00\x00\x00\xc0\x92\x17\x00\x01\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00'

Somewhere close to the middle, I can see \x01, \x02...etc. However, here are my other questions:

  1. At the beginning, I can see two other bytes changing, what are those values?

  2. Except for those \x00, I can see a few other bytes like ...\xc0\x92\x17\x00\x01... how to interpret those values?

  3. Is there any resource available for me to learn how python store variables in memory?

Solution

  • Download the Python C sources and study them. You'll see that "almost everything" is a PyObject* -- a pointer to a PyObject struct. The \x01 &c you see are just random bytes within some of those pointers, nothing to do with the 1,2,3 tuple you're seeing, not directly at least!