Increase certain elements by 1 in a list in Python

Question

I want to increase certain elements in I1 by 1 according to locations specified by T . I present the current and expected outputs.

I1= [17, 19, 30, 31, 34, 46]

T=[1, 5]

New=[i+1 for i in I1 if i in T]
print(New)

The current output is

[]

The expected output is

I1= [17, 20, 30, 31, 34, 47]

Answer 1

Use enumerate and if/else in list_comprehension .

# We can save a set of T if we have repeated items in 'T' and if 'I1' is a large array
set_T = set(T)

New = [item+1 if idx in set_T else item for idx, item in enumerate(I1)]
print(New)

Output: [17, 20, 30, 31, 34, 47]

Answer 2

This sort of thing is much easier in numpy:

I1 = np.array(I1)
I1[T] += 1