Python List Operations: Indexing, Slicing, and Modification

The article introduces Python lists, emphasizing that list elements may be of any type such as strings, tuples, dictionaries, functions, file objects, or numbers.

Lists can be accessed by index from the start (positive numbers) or from the end (negative numbers), and slices can be used to obtain sub‑lists.

>> x = ["first","sec","third","fourth"]

>> x[0]

returns

'first'

>> x[1]

returns

'sec'

>> x[2]

returns

'third'

>> x[3]

returns

'fourth'

>> x[0:3]

yields

['first', 'sec', 'third']

>> x[0:4]

yields

['first', 'sec', 'third', 'fourth']

>> x[-1]

returns

'fourth'

>> x[-2]

returns 'third' Positive indexes start at 0 for the first element, while negative indexes start at -1 for the last element.

Positive index

0

1

2

3

Negative index

-4

-3

-2

-1

Elements can be added, removed, or replaced, and slices can be assigned new values, causing the list size to adjust automatically.

>> x = [1,2,3,4,5,6,7,8,9]

>> x[1] = "two"

>> x[8:9] = []

>> x

results in

[1, 'two', 3, 4, 5, 6, 7, 8]

>> x[5:7] = [6.0,6.5,7.0]

>> x

becomes [1, 'two', 3, 4, 5, 6.0, 6.5, 7.0, 8] If the new slice size differs from the original, the list automatically resizes.

Common list operations include built‑in functions ( len, max, min), operators ( in, +, *), the del statement, and methods such as append, count, extend, index, insert, pop, remove, reverse, and sort. >> len(x) returns

9

>> [-1,0] + x

yields

[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>> x.reverse()

changes the list to [9, 8, 7, 6, 5, 4, 3, 2, 1] The + and * operators create new lists, leaving the original unchanged; list methods are invoked using the dot notation, e.g., x.method(arguments).

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