memoryview objects allow Python code to access the internal data of an object that supports the buffer protocol without copying. Memory is generally interpreted as simple bytes.
The documentation on memoryview can be found here
Questions tagged [memoryview]
144 questions
125
votes
6 answers
What exactly is the point of memoryview in Python?
Checking the documentation on memoryview:
memoryview objects allow Python code to access the internal data of an
object that supports the buffer protocol without copying.
class memoryview(obj)
Create a memoryview that references obj. obj must…
Basel Shishani
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43
votes
4 answers
Cython Numpy warning about NPY_NO_DEPRECATED_API when using MemoryView
I am converting a Cython memoryview to a numpy array (to be able to use it in pure Python code):
from libc.stdlib cimport realloc
cimport numpy as np
DTYPE = np.float64
ctypedef np.float64_t DTYPE_t
cpdef np.ndarray[DTYPE_t] compute(DTYPE_t[:,::1]…
Amenhotep
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2 answers
When should a memoryview be used?
The full description of memoryview can be found here:
Create a memoryview that references obj. obj must support the buffer protocol. Built-in objects that support the buffer protocol include bytes and bytearray.
A memoryview has the notion of an…
zr.
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28
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1 answer
Cython: Convert memory view to NumPy array
How to convert a typed memoryview to an NumPy array in cython? The docs have
cimport numpy as np
import numpy as np
numpy_array = np.asarray( my_pointer)
I took this for my case
np.asarray(…
embert
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26
votes
1 answer
Cython typed memoryviews: what they really are?
The Cython documentation explains very well what they allow for, how you can declare them, and how to use them.
However, it is still not clear to me what they really are. For example, a simple assignment from a numpy array like this:
my_arr =…
Gioker
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3 answers
Cython: Buffer type mismatch, expected 'int' but got 'long'
I'm having trouble passing in this memoryview of integers into this (rather trivial) function. Python is giving me this error:
ValueError: Buffer dtype mismatch, expected 'int' but got 'long'
Can someone help me understand what's going on?…
hlin117
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Why does creating this memoryview raise a ValueError only when assigning to a variable?
Pythons memoryview does not support datetime64 or timedelta. Ok. But when I try to create a memoryview of a structured array that includes a datetime64 or timedelta, it appears to work... unless I assign it to a variable!
In [19]:…
gerrit
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Cython Memoryview as return value
Consider this dummy Cython code:
#!python
#cython: boundscheck=False
#cython: wraparound=False
#cython: initializedcheck=False
#cython: cdivision=True
#cython: nonecheck=False
import numpy as np
# iterator function
cdef double[:] f(double[:]…
HenriV
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2 answers
How to use Cython typed memoryviews to accept strings from Python?
How can I write a Cython function that takes a byte string object (a normal string, a bytearray, or another object that follows the buffer protocol) as a typed memoryview?
According to the Unicode and Passing Strings Cython tutorial page, the…
Richard Hansen
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4 answers
Cython: Create memoryview without NumPy array?
Since I found memory-views handy and fast, I try to avoid creating NumPy arrays in cython and work with the views of the given arrays. However, sometimes it cannot be avoided, not to alter an existing array but create a new one. In upper functions…
embert
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11
votes
2 answers
Buffers and Memoryview Objects explained for the non-C programmer
Python 2.7 has introduced a new API for buffers and memoryview objects.
I read the documentation on them and I think I got the basic concept (accessing the internal data of an object in a raw form without copying it, which I suppose means a "faster…
mac
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Cython: Memory view of freed memory
In Cython code, I can allocate some memory and wrap it in a memory view, e.g. like this:
cdef double* ptr
cdef double[::1] view
ptr = PyMem_Malloc(N*sizeof('double'))
view = ptr
If I now free the memory using PyMem_Free(ptr),…
jmd_dk
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Shared memory in mpi4py
I use a MPI (mpi4py) script (on a single node), which works with a very large object. In order to let all processes have access to the object, I distribute it through comm.bcast(). This copies the object to all processes and consumes a lot of…
Roman
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How to create a memoryview for a non-contiguous memory location?
I have a fragmented structure in memory and I'd like to access it as a contiguous-looking memoryview. Is there an easy way to do this or should I implement my own solution?
For example, consider a file format that consists of records. Each record…
molnarg
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How to declare 2D c-arrays dynamically in Cython
I need to perform a lot of work using 2D numpy arrays of various sizes and I would like to offload these calculations onto cython. The idea is that my 2D numpy arrays would be passed from python to cython where it would be converted into c-array or…
phil_thy
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