x = ["one", "two", "three", "four"]

x[0]

'one'

x[1]

'two'

x[2]

'three'

len(x)

x[len(x) - 1]

'four'

x[-1]

'four'

x[-2]

'three'

x[-3]

'two'

x[-4]

'one'

x[3]

'four'

x[4]

    ---------------------------------------------------------------------------

    IndexError                                Traceback (most recent call last)

    <ipython-input-12-cedd7ac36334> in <module>
    ----> 1 x[4]
    
    IndexError: list index out of range

x[-5]

    ---------------------------------------------------------------------------

    IndexError                                Traceback (most recent call last)

    <ipython-input-13-3f8aa68a9513> in <module>
    ----> 1 x[-5]
    
    IndexError: list index out of range

['one', 'two', 'three', 'four']

x[-1] = 4

['one', 'two', 'three', 4]

type(x[-1])

int

type(x[0])

str

x[0] = x[0].upper()

['ONE', 'two', 'three', 4]

x[-1] = "four"

numbers = x

[num.upper() for num in numbers]

['ONE', 'TWO', 'THREE', 'FOUR']

numbers[0]

'ONE'

numbers[0][0]

'O'

numbers[1][2]

'o'

numbers

['ONE', 'two', 'three', 'four']