Expression that returns mutated list

January 27, 2023

I’m looking for a single expression, mutates an element and returns the modified list

The following is a bit verbose

# key=0; value=3; rng=[1,2]
[(v if i != key else value) for i, v in enumerate(rng)]

Edit:

I’m looking for a way to inline the following function in a single expression

def replace(rng: List, key: int, value):
    a = list(rng) 
    a[key] = value
    return a

>Solution :

Try list concatenation:

key = 0
value = 3
rng = [1, 2]

out = rng[:key] + [value] + rng[key+1:]
print(out)

rng[:key] is a copy of the list up to the key (exclusive), [value] is a new list where the only element is value, and rng[key+1] is a copy of the list from the key on (exclusive). Concatenate these together, and you get a copy where the key is replaced.