When you call the object.__repr__()
method in Python you get something like this back:
<__main__.Test object at 0x2aba1c0cf890>
Is there any way to get a hold of the memory address if you overload __repr__()
, other then calling super(Class, obj).__repr__()
and regexing it out?
This question is related to
python
object
memory-address
repr
While it's true that id(object)
gets the object's address in the default CPython implementation, this is generally useless... you can't do anything with the address from pure Python code.
The only time you would actually be able to use the address is from a C extension library... in which case it is trivial to get the object's address since Python objects are always passed around as C pointers.
You could reimplement the default repr this way:
def __repr__(self):
return '<%s.%s object at %s>' % (
self.__class__.__module__,
self.__class__.__name__,
hex(id(self))
)
With ctypes, you can achieve the same thing with
>>> import ctypes
>>> a = (1,2,3)
>>> ctypes.addressof(a)
3077760748L
Documentation:
addressof(C instance) -> integer
Return the address of the C instance internal buffer
Note that in CPython, currently id(a) == ctypes.addressof(a)
, but ctypes.addressof
should return the real address for each Python implementation, if
Edit: added information about interpreter-independence of ctypes
I know this is an old question but if you're still programming, in python 3 these days... I have actually found that if it is a string, then there is a really easy way to do this:
>>> spam.upper
<built-in method upper of str object at 0x1042e4830>
>>> spam.upper()
'YO I NEED HELP!'
>>> id(spam)
4365109296
string conversion does not affect location in memory either:
>>> spam = {437 : 'passphrase'}
>>> object.__repr__(spam)
'<dict object at 0x1043313f0>'
>>> str(spam)
"{437: 'passphrase'}"
>>> object.__repr__(spam)
'<dict object at 0x1043313f0>'
There are a few issues here that aren't covered by any of the other answers.
First, id
only returns:
the “identity” of an object. This is an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same
id()
value.
In CPython, this happens to be the pointer to the PyObject
that represents the object in the interpreter, which is the same thing that object.__repr__
displays. But this is just an implementation detail of CPython, not something that's true of Python in general. Jython doesn't deal in pointers, it deals in Java references (which the JVM of course probably represents as pointers, but you can't see those—and wouldn't want to, because the GC is allowed to move them around). PyPy lets different types have different kinds of id
, but the most general is just an index into a table of objects you've called id
on, which is obviously not going to be a pointer. I'm not sure about IronPython, but I'd suspect it's more like Jython than like CPython in this regard. So, in most Python implementations, there's no way to get whatever showed up in that repr
, and no use if you did.
But what if you only care about CPython? That's a pretty common case, after all.
Well, first, you may notice that id
is an integer;* if you want that 0x2aba1c0cf890
string instead of the number 46978822895760
, you're going to have to format it yourself. Under the covers, I believe object.__repr__
is ultimately using printf
's %p
format, which you don't have from Python… but you can always do this:
format(id(spam), '#010x' if sys.maxsize.bit_length() <= 32 else '#18x')
* In 3.x, it's an int
. In 2.x, it's an int
if that's big enough to hold a pointer—which is may not be because of signed number issues on some platforms—and a long
otherwise.
Is there anything you can do with these pointers besides print them out? Sure (again, assuming you only care about CPython).
All of the C API functions take a pointer to a PyObject
or a related type. For those related types, you can just call PyFoo_Check
to make sure it really is a Foo
object, then cast with (PyFoo *)p
. So, if you're writing a C extension, the id
is exactly what you need.
What if you're writing pure Python code? You can call the exact same functions with pythonapi
from ctypes
.
Finally, a few of the other answers have brought up ctypes.addressof
. That isn't relevant here. This only works for ctypes
objects like c_int32
(and maybe a few memory-buffer-like objects, like those provided by numpy
). And, even there, it isn't giving you the address of the c_int32
value, it's giving you the address of the C-level int32
that the c_int32
wraps up.
That being said, more often than not, if you really think you need the address of something, you didn't want a native Python object in the first place, you wanted a ctypes
object.
Just use
id(object)
Just in response to Torsten, I wasn't able to call addressof()
on a regular python object. Furthermore, id(a) != addressof(a)
. This is in CPython, don't know about anything else.
>>> from ctypes import c_int, addressof
>>> a = 69
>>> addressof(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: invalid type
>>> b = c_int(69)
>>> addressof(b)
4300673472
>>> id(b)
4300673392
You can get something suitable for that purpose with:
id(self)
Source: Stackoverflow.com