Python Language Dictionary: Difference between revisions

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Individual dictionary elements can be accessed with the <code>[...]</code> syntax or with the <code>get()</code> function.  
Individual dictionary elements can be accessed with the <code>[...]</code> syntax or with the <code>get()</code> function.  


===<tt>[]</tt> Syntax===
===Access with <tt>[]</tt> Syntax===


===<tt>get() Function===
===<tt>get() Function===

Revision as of 20:05, 16 February 2022

Internal

Overview

A dictionary is a mutable collection of key-value pairs. The pairs can be accessed and modified. Each key is unique within the key set, and can be an instance of any immutable type: boolean, integer, float, tuple, string, etc. In other programming languages, the same data structure is referred to as "associative array" or "hash tables" or "hash maps".

Key Discussion

The keys 1 and True are equivalent. Why?

Create a Dictionary

A new dictionary instance is declared using the {...} syntax. The curly braces are placed around comma-separated key: value pairs. The dictionary can be empty

d = {}

or it can be populated with values:

d = {'a': 'b', 1: 2}

It is good form to insert a space after :. A comma is tolerated after the last pair.

Access a Dictionary

Access Individual Elements

Individual dictionary elements can be accessed with the [...] syntax or with the get() function.

Access with [] Syntax

get() Function

[], get()

An attempt to access an inexistent key ends up in a KeyError exception being thrown.

Test the existence of a key.

Access:

d["key"]

Get All Keys

Get All Values

Modify a Dictionary

Modify Individual Elements

Add, modify, delete.

Combine Dictionaries