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pythonarraysnumpyshallow-copy

Creating numpy shallow copies with arithmetic operations

I noticed that array operations with an identity elements return a copy (possibly a shallow copy) of the array.

Consider the code snippet below.

a=np.arange(16).reshape([4,4])
print(a)
b=a+0
print(b)
a[2,2]=200
print(a)
print(b)

We see that b is a shallow copy of a. I don't know if it is a deep copy, because I think matrix is a subtype of array, rather than array of arrays.

If I only need a shallow copy,

  • Is there a difference between using np.copy() and arithmetic operations?
  • Is b=a+0 or b=a*1 a bad practice? If it is, why?

I know this is a frequently asked topic, but I couldn't find an answer for my particular question.

Thanks in advance!

Solution

  • Is there a difference between using np.copy() and arithmetic operations?

    Yes, consider following example

    import numpy as np
arr = np.array([[True,False],[False,True]])
arr_c = np.copy(arr)
arr_0 = arr + 0
print(arr_c)
print(arr_0)

    output

    [[ True False]
 [False  True]]
[[1 0]
 [0 1]]

    observe that both operations are legal (did not cause exception or error) yet give different results.