Singleton Design Pattern
Videos
| Section | Video Links |
|---|---|
| Singleton Overview |    |
| Singleton Use Case | |
| Python Dictionary | |
Book
Overview
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Singleton UML Diagram
Output
python ./singleton/singleton_concept.py id(Singleton) = 2164775087968 id(OBJECT1) = 2164775087968 id(OBJECT2) = 2164775087968 id(OBJECT3) = 2164775087968
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Example Use Case
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Example UML Diagram
Output
python ./singleton/client.py -----------Leaderboard----------- | 1 | Emmy | | 2 | Cosmo | | 3 | Sean | -----------Leaderboard----------- | 1 | Emmy | | 2 | Cosmo | | 3 | Sean | -----------Leaderboard----------- | 1 | Emmy | | 2 | Cosmo | | 3 | Sean |
New Coding Concepts
Python Dictionary
In the file /singleton/leaderboard.py,
"The Leaderboard as a Singleton" _table = {}
The {} is indicating a Python Dictionary.
A Dictionary can be instantiated using the curly braces {} or dict()
The Dictionary is similar to a List, except that the items are key:value pairs.
The Dictionary can store multiple key:value pairs, they can be changed, can be added and removed, can be re-ordered, can be pre-filled with key:value pairs when instantiated and is very flexible.
Since Python 3.7, dictionaries are ordered in the same way that they are created.
The keys of the dictionary are unique.
You can refer to the dictionary items by key, which will return the value.
PS> python >>> items = {"abc": 123, "def": 456, "ghi": 789} >>> items["abc"] 123
You can change the value at a key,
PS> python >>> items = {"abc": 123, "def": 456, "ghi": 789} >>> items["def"] = 101112 >>> items["def"] 101112
You can add new key:value pairs, and remove them by using the key.
PS> python >>> items = {"abc": 123, "def": 456, "ghi": 789} >>> items["jkl"] = 101112 >>> items["jkl"] 101112 >>> items.pop('def') 456 >>> items {'abc': 123, 'ghi': 789, 'jkl': 101112}
You can order a dictionary alphabetically by key
PS> python >>> items = {"abc": 123, "ghi": 789, "def": 456} >>> items {'abc': 123, 'ghi': 789, 'def': 456} >>> dict(sorted(items.items())) {'abc': 123, 'def': 456, 'ghi': 789}
Summary
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