How to modify list in python

Question

a = [1,2,3,4,5]

print(a)

for x in a:
x += 2

print(a)

How can I get all elements of a modified by 2 in this approach?

Answer 1

# in your code x is the element – not the index

for idx in range(len(a)):
a[idx] = a[idx] + 2

Answer 2

# Another Pythonic way is using "enumerate"

li = [1, 2, 3]
for idx, el in enumerate(li):
li[idx] = el + 2
print(li)

Answer 3

another way is to use map() and lambda function:

a = [1,2,3,4,5]
a = list(map(lambda x: x+2,a))

If you are not familiar with lambda functions:

def add_two(n):
return n+2

a = [1,2,3,4,5]
a = list(map(add_two,a))

https://www.programiz.com/JUMP_LINK__&&__python__&&__JUMP_LINK-programming/methods/built-in/map

Answer 4

just as a note:
list(map(...)) would create a new list.

Answer 5

Lisa
slightly different syntax based on preference
alternatively, one could also:

a = [1,2,3,4,5]
a = [i+2 for i in a]
print(a)

#or just

print([i+2 for i in a])

Answer 6

There exists also a numpy solution.

import numpy as np

a = [1,2,3,4,5]
a = list(np.array(a)+2)
#or leave it as an numpy array:
a = np.array(a) + 2

https://www.freecodecamp.org/news/the-ultimate-guide-to-the-numpy-scientific-computing-library-for-JUMP_LINK__&&__python__&&__JUMP_LINK/

Answer 7

Angelo Abi Hanna
How is that different from the previous suggestions?

Another way could be using list comprehension – but that actually creates a new list instead of modifying the existing one. 🤔

Answer 8

Yeah this approach is there.

I come from a c++ background where reference is there for an element

So curious whether range based for loop and accessing element using index is the only option to modify the list ?