Exercise N62 - There is an unnecessary code, Exercise N80 - IndexError

[Artur-Arstamyan]

Exercise 62 - Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? Code

a = np.random.randint(0, 10, (1, 3))
b = np.random.randint(0, 10, (3, 1))
it = np.nditer([a,b,None])

for x,y,z in it: 
    z = x + y

print(it.operands[2])

Unnecessary part

for x,y,z in it: 
    z = x + y

After it = np.nditer([a,b,None]) it.operands[2] already has that value.

Exercise N80 Current code that gives error

r = [slice(start,stop) for start,stop in zip(R_start,R_stop)]
z = [slice(start,stop) for start,stop in zip(Z_start,Z_stop)]
R[r] = Z[z]

Output

IndexError: only integers, slices (`:`), ellipsis (`...`), numpy.newaxis (`None`) and integer or boolean arrays are valid indices

Solution - Use tuples

r = tuple(slice(start,stop) for start,stop in zip(R_start,R_stop))
z = tuple(slice(start,stop) for start,stop in zip(Z_start,Z_stop))

[rougier]

Thanks.

• 62 I don't see a reason why operands[2] would hold the result and it doesn't on my machine.

>>> A = np.arange(3).reshape(3,1)
>>> B = np.arange(3).reshape(1,3)
>>> it = np.nditer([A,B,None])
>>> print(it.operands[2])
[[ 4607825790175356065 -4611042647052049243  4603322190547985584]
 [-4611042647052049244  4617283349392834114 -4613744806828471525]
 [ 4603322190547985580 -4613744806828471528  4606153024599475605]]
>>> for x,y,z in it: z[...] = x + y
>>> print(it.operands[2])
[[0 1 2]
 [1 2 3]
 [2 3 4]] 

• 80 You're right, can you make a PR?