Ch 9Lists — Class 11 Computer Science, concept-first.

A list is Python's workhorse container: an ordered sequence of values that is mutable, meaning its contents can be changed after it is created.

Individual elements of a list are picked out exactly the way characters are picked out of a string: write the list's name followed by the element's index in square brackets.

Lists in Python are mutable: the contents of a list can be changed after the list has been created. This is the single most important property separating a list from a string — a string, once built, c…

The list data type lets you manipulate its contents through a family of operations, each covered in its own sub-section:

Python joins two or more lists using the concatenation operator, written with the symbol +. The result is a single new list containing the elements of the first list followed by the elements of the se…

Python can replicate a list using the repetition operator, written with the symbol . Multiplying a list by an integer n produces a new list in which the original elements are repeated n times over, in…

Just as with strings, Python provides membership operators to ask whether a value occurs in a list. There are two of them, and each returns a Boolean result — True or False.

The slicing operation that extracts substrings from a string applies to lists as well: list[start:stop] returns a new list containing the elements from index start up to but not including index stop.

Traversing a list means visiting each of its elements, one after another — usually to print, examine or process them. Python offers two loop constructs for this: the for loop and the while loop.

The list data type comes with a rich set of built-in methods and functions for everyday programming: measuring a list, building one, adding and removing elements, searching, rearranging, and summarisi…

When a list appears as an element of another list, the inner list is called a nested list. Nesting lets one list carry structured sub-groups of data alongside ordinary elements.

Copying a list is one of the places where Python's behaviour surprises beginners: the "obvious" way — plain assignment — does not create a copy at all.

When a list is passed as an argument to a function, what we actually pass is a reference to the list — not a fresh copy of it.

This closing section pulls the whole chapter together: creating lists, and applying the operations and methods learnt so far, inside complete working programs.

- Lists are mutable sequences in Python — the elements of a list can be changed after the list is created.