ctypes.cast.
>>> import ctypes
>>> c_long_p = ctypes.POINTER(ctypes.c_long)
>>> some_long = ctypes.c_long(42)
>>> ctypes.addressof(some_long)
4300833936
>>> ctypes.cast(4300833936, c_long_p)
<__main__.LP_c_long object at 0x1005983b0>
>>> ctypes.cast(4300833936, c_long_p).contents
c_long(42)
tentacles666
tentacles666.wordpress.com › 2012 › 01 › 21 › python-ctypes-dereferencing-a-pointer-to-a-c
Python ctypes: dereferencing a pointer to a C structure | tentacles666
March 19, 2013 - First, you need to define a Python class that represents struct foo: class Foo (ctypes.Structure): _fields_ = [ ("bar", c_int) ] Next, you need to tell ctypes that newfoo() returns a pointer to such a thing: mylib.newfoo.restype = POINTER(Foo) Finally, after invoking newfoo(), you need to use the pointer’s contents member to dereference it: p = mylib.newfoo() p.contents.bar = 17 ·
python - Dereference void pointer to numpy array or list - Stack Overflow
However, this gives me back nonsense values, because the pointer dereference in _void_array_to_nested_list is wrong. The solution doesn't have to use NumPy, but that seems like the best approach. ... A minimal reproducible example would be useful. Have you verified somehow that the function ... More on stackoverflow.com
python - Is it possible to dereference variable id's? - Stack Overflow
Can you dereference a variable id retrieved from the id function in Python? For example: dereference(id(a)) == a I want to know from an academic standpoint; I understand that there are more practi... More on stackoverflow.com
[FEAT] being able to enforce the dereferencing of the smart pointer in argument conversion
I have a relatively complex ("externally given") class with a funny ownership model, so things can go missing while Python has a reference. To wrap it in Python safely, I'm trying to hold instances in a smart pointer (a la shared_ptr) that checks on dereferencing whether the referred to object ... More on github.com
21
December 29, 2020Why is there no concept of a pointer or pass-by reference in python? Is there something I can use
Holy cow calm down. EXCEPT THERE IS NO TRUE MULTITHREADING Lol yes there is. The threading module makes real threads. If you are upset about the GIL you just need to learn how to use it. why is there no pointers!? All python names are pointers. It's incredibly hard not to use a pointer. No idea what you are doing but if you mutate a dictionary in a function you will see it in the calling scope. >>> def add_data(d): ... d['Fuck-Me-With-RAM'] = 'pure zen' ... >>> data = {} >>> add_data(data) >>> data {'Fuck-Me-With-RAM': 'pure zen'} Read this: https://nedbatchelder.com/text/names.html this junk language Cheers, don't let the door hit ya More on reddit.com
16
0
August 10, 2022Medium
medium.com › @mengdaliu › moving-from-a-programming-language-eg-cf114c403607
Pointers in Python v.s. Pointers in Golang | by Shar-Pei Dog | Medium
June 17, 2019 - For example, if the variable dHome is declared to be of the type *Dog, we can assign it to some address by the statement dHome = &d, where d is a name to an existing dog, or dHome = &Dog{color : “red”, size: 100,}. By adding a * to the front ...
Python
docs.python.org › 2.5 › lib › ctypes-pointers.html
14.14.1.14 Pointers
December 23, 2008 - >>> null_ptr = POINTER(c_int)() >>> print bool(null_ptr) False >>> ctypes checks for NULL when dereferencing pointers (but dereferencing non-NULL pointers would crash Python):
PyPI
pypi.org › project › pointers.py › 1.0.5
pointers.py
JavaScript is disabled in your browser. Please enable JavaScript to proceed · A required part of this site couldn’t load. This may be due to a browser extension, network issues, or browser settings. Please check your connection, disable any ad blockers, or try using a different browser
Real Python
realpython.com › pointers-in-python
Pointers in Python: What's the Point? – Real Python
March 18, 2026 - Pointers are widely used in C and C++. Essentially, they are variables that hold the memory address of another variable. For a refresher on pointers, you might consider checking out this overview on C Pointers. In this article, you’ll gain a better understanding of Python’s object model and learn why pointers in Python don’t really exist.
GeeksforGeeks
geeksforgeeks.org › using-pointers-in-python-using-ctypes
Using Pointers in Python using ctypes - GeeksforGeeks
January 9, 2023 - We will see how we can use Pointers in Python programming language using the ctypes module. Some basic operations like storing addresses, pointing to a different variable using pointers, etc. will be demonstrated here.
Sololearn
sololearn.com › en › Discuss › 1609533 › what-is-the-difference-between-dereference-and-pointers
What is the difference between dereference and pointers? | Sololearn: Learn to code for FREE!
December 4, 2018 - ... Hi there, Reference is just a alias name for some variable they are technically same variables but with different name Example : int a = 10; int &b = a ; {Value of b will be = 10} Changing "b" will cause "a" to change A pointer is a variable ...
Google Groups
groups.google.com › g › cython-users › c › uul_h95lKqM
cannot dereference pointer
I want the python-to-C type > conversion to occur and assign to the appropriate dereferenced C > value. > > cdef void* convert_multiplier(int gtype, value, > int *iv, long *lv, long long *llv, float *fv, double *dv): > if gtype == C_INT: > if value: > *iv = value ... http://docs.cython.org/src/userguide/language_basics.html#differences-between-c-and-cython-expressions · The unary '*' operator has a different meaning in Python.
Top answer 1 of 2
2
I can't test this right now, but this is what I would try:
import numpy as np
result = ...
shape = (10, 2)
array_size = np.prod(shape)
mem_size = 8 * array_size
array_str = ctypes.string_at(result, mem_size)
array = np.frombuffer(array_str, float, array_size).reshape(shape)
array will be read only, copy it if you need a writable array.
2 of 2
2
Here is a solution that uses ctypes.cast or numpy.ctypeslib.as_array, and no ctypes.string_at just in case if it makes an extra copy of memory region.
class _FFIArray(Structure):
_fields_ = [("data", c_void_p), ("len", c_size_t)]
class Coordinate(Structure):
_fields_ = [("latitude", c_double), ("longitude", c_double)]
class Coordinates(Structure):
_fields_ = [("data", POINTER(Coordinate)), ("len", c_size_t)]
decode_polyline = lib.decode_polyline_ffi
decode_polyline.argtypes = (c_char_p, c_uint32)
decode_polyline.restype = _FFIArray
# assuming that the second argument is the length of polyline,
# although it should not be needed for `\0` terminated string
res = decode_polyline(polyline, len(polyline))
nres = Coordinates(cast(res.data, POINTER(Coordinate)), res.len)
for i in range(nres.len):
print(nres.data[i].latitude, nres.data[i].longitude)
# if just a numpy (np) array is needed
xs = np.ctypeslib.as_array((c_double * res.len * 2).from_address(res.data))
# "New view of array with the same data."
xs = xs.view(dtype=[('a', np.float64), ('b', np.float64)], type=np.ndarray)
xs.shape = res.len
Duke
jupyternotebooks-dpb6-e8e09e2d24a591fa64baaf90dc750c5415a29cf5e.pages.oit.duke.edu › 3-CPlusCPlus › 13-Pointers › 13-Pointers.html
13. Pointers — Programming for Financial Technology
To access the contents of the memory location that a pointer references, we use the unary operator * (dereferences). Going back to the third Python notebook, you can equate this address to the address of a building in a city - it just references a location in memory.
Top answer 1 of 4
58
Here's a utility function based on a (now-deleted) comment made by "Tiran" in a weblog discussion @Hophat Abc references in his own answer that will work in both Python 2 and 3.
Disclaimer: If you read the the linked discussion, you'll find that some folks think this is so unsafe that it should never be used (as likewise mentioned in some of the comments below). I don't agree with that assessment but feel I should at least mention that there's some debate about using it.
import _ctypes
def di(obj_id):
""" Inverse of id() function. """
return _ctypes.PyObj_FromPtr(obj_id)
if __name__ == '__main__':
a = 42
b = 'answer'
print(di(id(a))) # -> 42
print(di(id(b))) # -> answer
2 of 4
11
Not easily.
You could recurse through the gc.get_objects() list, testing each and every object if it has the same id() but that's not very practical.
The id() function is not intended to be dereferenceable; the fact that it is based on the memory address is a CPython implementation detail, that other Python implementations do not follow.
Naukri
naukri.com › code360 › library › dereference-pointers
Dereference Pointers - Naukri Code 360
Almost there... just a few more seconds
Llllllllll
llllllllll.github.io › principles-of-performance › python-overview.html
Python Overview — principles-of-performance documentation
Because the size of each value differs depending on the type, which cannot be known ahead of time because Python is dynamically typed, Python just refers to all objects through a pointer to the value struct. All we know is that the first member of the value struct will be a pointer to some collection of functions which will be designed to know the true size of the object and how to interpret the data. This means that at minimum we must do one memory dereference to perform any operation on a Python object.
GitHub
github.com › pybind › pybind11 › issues › 2751
[FEAT] being able to enforce the dereferencing of the smart pointer in argument conversion · Issue #2751 · pybind/pybind11
December 29, 2020 - I have a relatively complex ("externally given") class with a funny ownership model, so things can go missing while Python has a reference. To wrap it in Python safely, I'm trying to hold instances in a smart pointer (a la shared_ptr) that checks on dereferencing whether the referred to object still exists.
Author: pybind
Python Morsels
pythonmorsels.com › pointers
Variables and objects in Python - Python Morsels
February 28, 2022 - Variables in Python are not buckets containing things; they're pointers (they point to objects). The word "pointer" may sound scary, but a lot of that scariness comes from related concepts (e.g. dereferencing) which aren't relevant in Python.
Rosetta Code
rosettacode.org › wiki › Pointers_and_references
Pointers and references - Rosetta Code
February 6, 2026 - However this example will stick to the "proper" uses of pointer arithmetic, i.e. indexing and offsetting. add bx, 2 ;add 2 to bx. bx contains the memory address of the first "l" in "Hello" mov al,[ds:bx] ;dereference the pointer and store the ...
Python
bugs.python.org › issue24044
Issue 24044: NULL pointer dereference in listsort() with key function - Python tracker
April 23, 2015 - This issue tracker has been migrated to GitHub, and is currently read-only. For more information, see the GitHub FAQs in the Python's Developer Guide · This issue has been migrated to GitHub: https://github.com/python/cpython/issues/68232
Reddit
reddit.com › r/learnpython › why is there no concept of a pointer or pass-by reference in python? is there something i can use
r/learnpython on Reddit: Why is there no concept of a pointer or pass-by reference in python? Is there something I can use
August 10, 2022 -
I am a C++ and assembly developer mainly, but as someone entering the job market that just doesn't cut it. I have a job I got hired for where I'm taking 4+ years of a python codebase that no one has documented and is spaghetti and updating it, and was supposed to be adding multithreading (EXCEPT THERE IS NO TRUE MULTITHREADING SO I HAVE TO DO MULTIPROCESSING WHICH IS A CLUSTER-F***). So that blows.
BUT
why is there no pointers!? or way to go references? I need to store data in an object that gets passed into some libraries, and then the library runs callbacks where I analyze the crap. From there I need to set the values so in other callbacks I can work with the values. It's a dictionary so I can add some new keys to store the data... except I can't because it's like pass by value so the data instantly gets deleted once it returns from the callback. If I passed in a pointer I'd be set, except that's not possible...
That's just one issue in a mirad of issues I'm facing with this junk language. Not to even mention the horribleness of everything using like 2gb of memory because each process copies the entire memory space of the head process....
Please tell me there's some kinda object or pointer thing I can use.
EDIT : I got the help I needed here, thanks everyone! sorry to trash the language a bit above I was just frustrated lol
Top answer 1 of 4
13
Holy cow calm down. EXCEPT THERE IS NO TRUE MULTITHREADING Lol yes there is. The threading module makes real threads. If you are upset about the GIL you just need to learn how to use it. why is there no pointers!? All python names are pointers. It's incredibly hard not to use a pointer. No idea what you are doing but if you mutate a dictionary in a function you will see it in the calling scope. >>> def add_data(d): ... d['Fuck-Me-With-RAM'] = 'pure zen' ... >>> data = {} >>> add_data(data) >>> data {'Fuck-Me-With-RAM': 'pure zen'} Read this: https://nedbatchelder.com/text/names.html this junk language Cheers, don't let the door hit ya
2 of 4
4
EXCEPT THERE IS NO TRUE MULTITHREADING SO I HAVE TO DO MULTIPROCESSING WHICH IS A CLUSTER-F*** If that's an issue for you then someone used the wrong tool for the wrong job. That said: most of the time asyncio's single-threaded event loop will do just fine. why is there no pointers!? Why should there be? It's a high-level language with a garbage collector. or way to go references? For any collection type or class you're already getting effectively pass-by-reference, but if you mean why won't def foo(x): x = 2 x = 1 foo(x) # x is still 1 here change x to 2: because in python there's no reason it should. Spooky action at a distance is generally discouraged and, just like in C/C++ you should avoid when you reasonably can. It's a dictionary so I can add some new keys to store the data... except I can't because it's like pass by value so the data instantly gets deleted once it returns from the callback. Dictionaries are not passed by value. def foo(x): x["new_key"] = "it's here" y = {} foo(y) print(y) A bit more technically: everything is effectively passed by reference, the language simply (deliberately) has immutable values for integers, floats, strings, and most 'primitive' types like that so there exists no way to express the concept of "edit the value of the python object this variable currently points at" for those primitives. The concept absolutely does exist for objects in general - anything done via the name (as opposed to reassigning the name) acts on the underlying python object. That's why the dictionary key is persisted in y outside the function in my example.
Top answer 1 of 11
86
This can be done explicitly.
class ref:
def __init__(self, obj): self.obj = obj
def get(self): return self.obj
def set(self, obj): self.obj = obj
a = ref([1, 2])
b = a
print(a.get()) # => [1, 2]
print(b.get()) # => [1, 2]
b.set(2)
print(a.get()) # => 2
print(b.get()) # => 2
2 of 11
24
You may want to read Semantics of Python variable names from a C++ perspective. The bottom line: All variables are references.
More to the point, don't think in terms of variables, but in terms of objects which can be named.