Python replace first character in every element of a list

Yes, strings are immutable in Python. That means you have to build a new string to replace the old one. And you have to store that new string—either back in the original list, or in a new list.

If you want to store them back in the original list, you need the index as well as the value:

for idx, i in enumerate(list1):
    list[idx] = i[1:]

If you want to create a new list, you just append them as they come in, or use a comprehension:

list2 = []
for i in list1:
    list2.append(i[1:])

list2 = [i[1:] for i in list1]

Usually creating a new list is better (which is why Python has a syntactic shortcut for only that one), but sometimes mutating in-place is better (which is why that one isn't too much more verbose or difficult). The question is: If any other piece of code had made another reference to list1, would you want it to see the changed version, or the original version?

You can do it with a list comprehension like this:

test_list = ['this', 'is', 'a', 'test']

first_letters = ['i','t','t','a']

[letter+word[1:] for letter, word in zip(first_letters, test_list)]

# ['ihis', 'ts', 't', 'aest']

The zip function essentially creates this list of tuples (it's actually an iterator of tuples, but for simplicity, it can be thought of as a list):

[('i', 'this'), ('t', 'is'), ('t', 'a'), ('a', 'test')]

Which the list comprehension iterates through, returning a new list with the letter (first element of each tuple) and all letters starting from the second letter of the word (second element of the tuple)

It is essentially equivalent to the following loop, if you prefer that syntax:

result = []

for letter, word in zip(first_letters, test_list):
    result.append(letter+word[1:])

you can try range method :

test_list = ['this', 'is', 'a', 'test']

first_letters = ['i','t','t','a']



print([first_letters[i]+test_list[i][1:]for i in range(len(test_list))])

output:

['ihis', 'ts', 't', 'aest']

x = ['this', 'is', 'a', 'test']
y = ['i','t','t','a']
z = [y + x[1:] for x, y in zip(x, y)]
print(z)

z = ['ihis', 'ts', 't', 'aest']