Ch 10Tuples and Dictionaries — Class 11 Computer Science, concept-first.

A tuple is an ordered sequence that can hold elements of different data types — integers, floats, strings, lists, and even other tuples.

Elements of a tuple are accessed exactly the way elements of a list or characters of a string are accessed — through indexing (and, as we will see later in the chapter, slicing).

A tuple is an immutable data type. Immutability means that once a tuple has been created, its elements cannot be changed.

Tuples support the same family of sequence operations you have already used with strings and lists. This section groups them into four operations, each covered in its own sub-section:

Concatenation joins tuples together using the + operator. Applying + to two tuples produces a longer tuple containing all the elements of the first followed by all the elements of the second.

The repetition operation is written with the symbol and repeats the elements of a tuple a given number of times.

The membership operators test whether a value occurs among a tuple's elements.

Slicing extracts a contiguous part of a tuple, exactly as it does for strings and lists. The general form is tuple[start : stop : step] — the slice begins at index start and runs up to but not includi…

Python ships with several ready-made functions and methods for working with tuples. Table 10.1 of the textbook collects the commonly used ones; each is explained below with its behaviour and a worked…

Tuple assignment (also called unpacking) is a very useful Python feature: a tuple of variables on the left side of the assignment operator receives, position by position, the corresponding values from…

A tuple placed inside another tuple is called a nested tuple. Nesting is the natural way to store a table of records: each inner tuple is one record (one row), and the outer tuple holds all the record…

This section puts tuples to work in three complete programs, each showing a practical tuple idiom: swapping values with tuple assignment, returning multiple values from a function, and growing a tuple…

The dictionary data type belongs to the mapping category of Python types. A dictionary is a mapping between a set of keys and a set of values — instead of numbering its contents by position the way a…

To create a dictionary, write its items separated by commas and enclosed in curly braces . Each item is a key-value pair with the key and value separated by a colon (:).

Sequences — strings, lists and tuples — are accessed by indexing: you ask for the item at a numbered position. Dictionaries work differently.

In sharp contrast to tuples, dictionaries are mutable — the contents of a dictionary can be changed after it has been created.

Adding a new item to a dictionary is a single assignment: put the new key in square brackets on the left and its value on the right.

An existing item of a dictionary is modified by simply overwriting the key-value pair: assign a new value to a key that is already present, and the old value is replaced.

Just as tuples support sequence operations, dictionaries come with operations of their own. The operation the book covers here is membership — testing whether a particular key is present in the dictio…

The membership operator in checks whether a key is present in the dictionary. It returns True if the key exists, else it returns False:

Traversing a dictionary means visiting each of its items one by one — and the tool for that is the for loop. The textbook shows two equivalent methods.

Python provides many built-in functions and methods for working with dictionaries. Table 10.2 of the textbook collects the commonly used ones; each is explained below with a worked example.

Having learnt how to create a dictionary and the methods that operate on it, this section applies those manipulation methods in four complete programs.

- Tuples are immutable sequences — once a tuple is created, its elements cannot be changed. - The elements of a tuple are written inside round brackets, separated by commas.