使用双方括号访问列表元素（python）

Question

given a list, such as:

programming_languages = ['Python', 'Perl', 'R', 'Ruby']

What are the rules for using double square brackets []?

What I mean is if I try accessing programming_languages[2][0] or programming_languages[3][0] or programming_languages[-1][-4] for example, I'll get the element 'R'.

Thanks in advance for the help on clearing this up for me!

Edit: For some reason I did not realise the 'R' I get while accessing programming_languages[3][0] or programming_languages[-1][-4] is actually the 1st character of the 4th element in the list, and NOT the 2nd element 'R'. Thanks for the answers below!

Answer 1

The square bracket operator isn't only defined on arrays, but also on strings.

a = programming_languages[1] # a = 'Perl'
print(a[0]) # P, which is the 0th letter of the string
print(a[3]) # l, which is the 3rd letter of the string

Answer 2

programming_languages is an array, so you are accessing each elemnt inside the array by first bracket, eg. : programming_languages[0] which returns 'Python' . noe in python, strings are considers as an array of characters, so the second bracket is picking the character whiting that string, so eg: programming_languages[0][0] returns 'P'

Answer 3

The square bracket syntax, like programming_languages[n] allow you to access the nth element.

programming_languages = ['Python', 'Perl', 'R', 'Ruby']
programming_languages[0] # getting the first element in the list
# Python

When you use double square bracket, it means your element is a list-like object. If the first elements is Python then the first element would be P

>>> programming_languages = ['Python', 'Perl', 'R', 'Ruby']
>>> # getting the first element in the list
>>> programming_languages[0] 
 Python
>>> # getting the first element in the string 'Python'
>>> programming_languages[0][0] 
 P