How to create an immutable Numpy array? : Pythoneo

Let’s check how to create an immutable Numpy array.

Setting writeable flag

To make the array immutable, you need to set the writeable flag to false.

import numpy as np

my_array = np.array([1, 2, 3])
print(my_array)

my_array[1] = 5
print(my_array)

my_array.flags.writeable = False

my_array[2] = 6
print(my_array)

As you can see, it is not possible to change the array. Python displays assignment destination is a read-only ValueError.

Traceback (most recent call last):
  File "C:\Users\pythoneo\PycharmProjects\pythoneoProject\immutable_array_python.py", line 11, in 
    my_array[2] = 6
ValueError: assignment destination is read-only

Setting a writeable flag rendered your code immutable.To turn off read-only mode, you need to set the writeable flag back to true.

Setting write flag

Alternatively, you can set the write flag to false.

import numpy as np

my_array = np.array([1, 2, 3])
print(my_array)

my_array[1] = 5
print(my_array)

my_array.setflags(write=False)

my_array[2] = 6
print(my_array)

Python displays ValueError as well. The full error message is as follows:

Traceback (most recent call last):
  File "C:\Users\pythoneo\PycharmProjects\pythoneoProject\immutable_array_python.py", line 11, in 
    my_array[2] = 6
ValueError: assignment destination is read-only

Set the write flag back to true to allow editing.

Key Takeaways

There are two ways to create an immutable Numpy array:
By setting the writeable flag to False
By setting the write flag to False

When the writeable flag is set to False, the array cannot be modified.

When the write flag is set to False, the array can still be modified, but only by creating a new array.

FAQ

Q: Why would I want to create an immutable Numpy array?
A: There are a few reasons why you might want to create an immutable Numpy array:
- To prevent accidental changes to the array.
- To improve performance, as immutable arrays are often faster than mutable arrays.
- To make the array thread-safe, as immutable arrays can be safely accessed by multiple threads without the risk of corruption.
Q: What is the difference between the writeable flag and the write flag?
The writeable flag controls whether the array can be modified. The write flag controls whether the array can be modified in-place.