Question

From an S.O answer:

“Don’t modify strings.

Work with them as lists; turn them into strings only when needed.

… code sample …

Python strings are immutable (i.e. they can’t be modified). There are a lot of reasons for this. Use lists until you have no choice, only then turn them into strings.”

Is this considered best practice?

I find it a bit odd that Python has methods that return new modified strings (such as upper(), title(), replace() etc.) but doesn’t have an insert method that returns a new string. Have I missed such a method?

Edit: I’m trying to rename files by inserting a character:

import os
for i in os.listdir('.'):
    i.insert(3, '_')

Which doesn’t work due to immutability. Adding to the beginning of a string works fine though:

for i in os.listdir('.'):
    os.rename(i, 'some_random_string' + i)

Edit2: the solution:

>>> for i in os.listdir('.'):                                                │··
...  os.rename(i, i[:4] + '_' + i[4:])

Slicing certainly is nice and solves my problem, but is there a logical explanation why there is no insert() method that returns a new string?

Thanks for the help.

Answer 1

If you want to insert at a particular spot, you can use slices and +. For example:

a = "hello"
b = a[:2] + '_S1M0N_' + a[2:]

then b will be equal to he_S1M0N_llo.