Accessing Object Memory Address

Question

When you call the object   repr     method in Python you get something like this back      lt   main   Test object at 0x2aba1c0cf890 gt      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

User · Answer

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>'

User · Answer

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

User · Answer

The Python manual has this to say about id        Return 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   Implementation note    this is the address of the object     So in CPython  this will be the address of the object  No such guarantee for any other Python interpreter  though   Note that if you re writing a C extension  you have full access to the internals of the Python interpreter  including access to the addresses of objects directly

User · Answer

With ctypes  you can achieve the same thing with   gt  gt  gt  import ctypes  gt  gt  gt  a    1 2 3   gt  gt  gt  ctypes addressof a  3077760748L   Documentation      addressof C instance  - gt  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   ctypes is supported memory pointers are a valid notion    Edit  added information about interpreter-independence of ctypes

User · Answer

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    lt   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

User · Answer

Just use   id object

User · Answer

You can get something suitable for that purpose with   id self

User · Answer

You could reimplement the default repr this way   def   repr   self       return   lt  s  s object at  s gt               self   class     module            self   class     name            hex id self

User · Answer

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    gt  gt  gt  from ctypes import c int  addressof  gt  gt  gt  a   69  gt  gt  gt  addressof a  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  invalid type  gt  gt  gt  b   c int 69   gt  gt  gt  addressof b  4300673472  gt  gt  gt  id b  4300673392

[python] Accessing Object Memory Address

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