Tips and Tricks

Getting the address of underlying C objects from the low-level bindings

All CUDA C types are exposed to Python as Python classes. For example, the CUstream type is exposed as a class with methods getPtr() and __int__() implemented.

There is an important distinction between the getPtr() method and the behaviour of __int__(). Since a CUstream is itself just a pointer, calling instance_of_CUstream.getPtr() returns the pointer to the pointer, instead of the value of the CUstream C object that is the pointer to the underlying stream handle. int(instance_of_CUstream) returns the value of the CUstream converted to a Python int and is the actual address of the underlying handle.

Warning

Using int(cuda_obj) to retrieve the underlying address of a CUDA object is deprecated and subject to future removal. Please switch to use get_cuda_native_handle() instead.

Lifetime management of the CUDA objects

All of the Python classes do not manage the lifetime of the underlying CUDA C objects. It is the user’s responsibility to use the appropriate APIs to explicitly destruct the objects following the CUDA Programming Guide.

Getting and setting attributes of extension types

While the bindings outwardly present the attributes of extension types in a pythonic way, they can’t always be interacted with in a Pythonic style. Often the getters/setters (__getitem__(), __setitem__()) are actually a translation step to convert values between Python and C. For example, in some cases, attempting to modify an attribute in place, will lead to unexpected behavior due to the design of the underlying implementation. For this reason, users should use the getters and setters directly when interacting with extension types.

An example of this is the CULaunchConfig type.

cfg = cuda.CUlaunchConfig()

cfg.numAttrs += 1
attr = cuda.CUlaunchAttribute()

...

# This works. We are passing the new attribute to the setter
drv_cfg.attrs = [attr]

# This does not work. We are only modifying the returned attribute in place
drv_cfg.attrs.append(attr)