Creating dictionary-like classes may be a requirement in your Python career. Specifically, you may be interested in making custom dictionaries with modified behavior, new functionalities, or both. In Python, you can do this by inheriting from an , by subclassing the built-in Show
In this tutorial, you’ll learn how to:
Additionally, you’ll code a few examples that’ll help you understand the pros and cons of using To get the most out of this tutorial, you should be familiar with Python’s built-in Join Now: Click here to join the Real Python Newsletter and you'll never miss another Python tutorial, course update, or post. Creating Dictionary-Like Classes in PythonThe built-in Sometimes, the standard functionality of Python dictionaries isn’t enough for certain use cases. In these situations, you’ll probably have to create a custom dictionary-like class. In other words, you need a class that behaves like a regular dictionary but with modified or new functionality. You’ll typically find at least two reasons for creating custom dictionary-like classes:
Note that you could also face situations in which you need to both extend and modify the dictionary’s standard functionality. Depending on your specific needs and skill level, you can choose from a few strategies for creating custom dictionaries. You can:
There are a few key considerations when you’re selecting the appropriate strategy to implement. Keep reading for more details. Remove adsBuilding a Dictionary-Like Class From an Abstract Base ClassThis strategy for creating dictionary-like classes requires that you inherit from an abstract base class (ABC), like . This class provides concrete generic implementations of all the dictionary methods except for , , , , and , which you’ll have to implement by yourself. Additionally, suppose you need to customize the functionality of any other standard dictionary method. In that case, you’ll have to override the method at hand and provide a suitable implementation that fulfills your needs. This process implies a fair amount of work. It’s also error-prone and requires advanced knowledge of Python and its data model. It can also imply performance issues because you’ll be writing the class in pure Python. The main advantage of this strategy is that the parent ABC will alert you if you miss any method in your custom implementation. For these reasons, you should embrace this strategy only if you need a dictionary-like class that’s fundamentally different from the built-in dictionary. In this tutorial, you’ll focus on creating dictionary-like classes by inheriting from the built-in Inheriting From the Python Built-in >>> numbers = UpperCaseDict({"one": 1, "two": 2, "three": 3}) >>> numbers {'one': 1, 'two': 2, 'three': 3} 7 ClassFor a long time, it was impossible to subclass Python types implemented in C. Python 2.2 fixed this issue. Now you can , including
The first item in this list may be a requirement for C code that expects a Python built-in class. The second item allows you to add new functionality on top of the standard dictionary behavior. Finally, the third item will enable you to restrict the attributes of a subclass to only those attributes predefined in Even though subclassing built-in types has several advantages, it also has some drawbacks. In the specific case of dictionaries, you’ll find a few annoying pitfalls. For example, say that you want to create a dictionary-like class that automatically stores all its keys as strings where all the letters, if present, are uppercase. To do this, you can create a subclass of >>> Cool! Your custom dictionary seems to work well. However, there are some hidden issues in this class. If you try to create an instance of >>> What just happened? Why doesn’t your dictionary convert the keys into uppercase letters when you call the class’s constructor? It looks like the class’s initializer, Unfortunately, this issue affects other dictionary methods, like and , for example: >>> Again, your uppercase functionality isn’t working well in these examples. To solve this issue, you must provide custom implementations of all the affected methods. For example, to fix the initialization issue, you can write an Here, With this update, the initialization process of your custom dictionary should work correctly. Go ahead and give it a try by running the following code: >>> Providing your own Why do That’s why subclassing the built-in Subclassing >>> numbers = UpperCaseDict({"one": 1, "two": 2, "three": 3}) >>> numbers {'one': 1, 'two': 2, 'three': 3} 8 From >>> numbers = UpperCaseDict() >>> numbers["one"] = 1 >>> numbers["two"] = 2 >>> numbers["three"] = 3 >>> numbers {'ONE': 1, 'TWO': 2, 'THREE': 3} >>> numbers.update({"four": 4}) >>> numbers {'ONE': 1, 'TWO': 2, 'THREE': 3, 'four': 4} >>> numbers.setdefault("five", 5) 5 >>> numbers {'ONE': 1, 'TWO': 2, 'THREE': 3, 'four': 4, 'five': 5} 2Starting with Python 1.6, the language has provided There are also other hidden differences. To uncover them, go back to your original implementation of >>> This time, instead of inheriting from >>> Now As you learned before, the most notable difference between Coding Dictionary-Like Classes: Practical ExamplesYou already know that subclasses of To work around this issue, you can inherit from Admittedly, when you think of creating a dictionary-like class, inheriting from Inheriting from The bottom line is that In any case, remember that You should consider several factors when deciding whether to inherit from
In the following section, you’ll experience the first three factors in this list by coding a few practical examples. You’ll learn about performance implications a bit later, in the section on . Remove adsA Dictionary That Accepts British and American Spelling of KeysAs the first example, say you need a dictionary that stores keys in American English and allows key lookup in either American or British English. To code this dictionary, you’ll need to modify at least two , The Because you need to modify the core behavior of the When you subclass Here’s the code that relies on In this example, you first define a constant, Then you define The Here’s how your >>> By subclassing If you have less code to write, then you’ll have less work to do. More importantly, you’ll be safer because less code often implies a lower risk of bugs and errors. Note: If you need that the keyword works with both spellings, then you’ll have to implement a custom The main drawback of this implementation is that if you someday decide to update The example below shows how to provide the same functionality as before using This implementation looks slightly different from the original one but works the same. It could also be harder to code because you’re not using The main advantage of this new implementation is that your class is now compatible with Note: Remember that if you inherit directly from It’s often more convenient to extend the standard dictionary functionality by subclassing A Dictionary That Accesses Keys Through ValuesAnother common requirement for a custom dictionary is to provide additional functionality apart from the standard behavior. For example, say that you want to create a dictionary-like class that provides methods to retrieve the key that maps to a given target value. You need a method that retrieves the first key that maps to the target value. You also want a method that returns an iterator over those keys that map to equal values. Here’s a possible implementation of this custom dictionary: This time, instead of inheriting from The As a generator method that yields keys on demand, Here’s how this dictionary works in practice: >>> Cool! Your In general, you should use On the other hand, if you just need a dictionary-like class with extended functionality that doesn’t affect or modify the core A Dictionary With Additional FunctionalitiesAs a final example of how to implement a custom dictionary with additional features, say that you want to create a dictionary that provides the following methods: MethodDescription To implement these three methods, you don’t need to modify the core behavior of the built-in Here’s the code that implements the required methods on top of In this example, Here’s how >>> In these examples, you first create an instance of Then, Considering PerformanceInheriting from To check if performance issues can arise when you inherit from Your classes should look something like this: The only difference between these two classes is that To check their performance, you can start by timing core dictionary operations, such as class instantiation. Run the following code in your Python interactive session: >>> In this code snippet, you use the module along with the Once you’ve run this time-measuring code, then you compare both initialization times. In this specific example, the initialization of the class based on Measuring the execution time of new functionalities may also be interesting. For example, you can check the execution time of >>> The performance difference between the class based on Often, when you create a custom dictionary by subclassing It’s worth noting if you’re aiming to modify the core dictionary functionality, then ConclusionNow you know how to create custom dictionary-like classes with modified behavior and new functionalities. You’ve learned to do this by subclassing the built-in In this tutorial, you learned how to:
You’ve also written some practical examples that helped you understand the pros and cons of using You’re now ready to create your custom dictionaries and to leverage the full power of this useful data type in Python in response to your coding needs. Join Now: Click here to join the Real Python Newsletter and you'll never miss another Python tutorial, course update, or post. Mark as Completed 🐍 Python Tricks 💌 Get a short & sweet Python Trick delivered to your inbox every couple of days. No spam ever. Unsubscribe any time. Curated by the Real Python team.  Send Me Python Tricks » About Leodanis Pozo Ramos Leodanis is an industrial engineer who loves Python and software development. He's a self-taught Python developer with 6+ years of experience. He's an avid technical writer with a growing number of articles published on Real Python and other sites. » More about LeodanisEach tutorial at Real Python is created by a team of developers so that it meets our high quality standards. The team members who worked on this tutorial are: Aldren Bartosz Geir Arne Kate Master Real-World Python Skills With Unlimited Access to Real Python Join us and get access to thousands of tutorials, hands-on video courses, and a community of expert Pythonistas: Level Up Your Python Skills » Master Real-World Python Skills Join us and get access to thousands of tutorials, hands-on video courses, and a community of expert Pythonistas: Level Up Your Python Skills » What Do You Think? Rate this article: Tweet Share Share EmailWhat’s your #1 takeaway or favorite thing you learned? How are you going to put your newfound skills to use? Leave a comment below and let us know. Commenting Tips: The most useful comments are those written with the goal of learning from or helping out other students. and get answers to common questions in our support portal. Apa itu dictionary di Python?4. Dictionary
Tipe data dictionary akan digunakan untuk memetakan sebuah nilai pada data ke dalam nilai lainnya. Tipe data dictionary dapat dideklarasikan dengan diawali oleh tanda kurung buka kurawal ( { ), memisahkan setiap elemen di dalamnya dengan tanda koma ( , ) dan ditutup dengan tanda kurung tutup ( } ).
Bagaimana cara mengakses tuple?Untuk mengakses nilai dalam Tuple, maka kamu bisa menggunakan tanda kurung siku untuk mengiris beserta indeks agar mendapatkan nilai yang tersedia pada indeks tersebut.
Apa fungsi dictionary?Dictionary merupakan tipe data pada Python yang berfungsi untuk menyimpan kumpulan data atau nilai, yang setiap urutanya berisi key dan value.
Jelaskan apa yang dimaksud dengan key value pada Dictionary?Data dictionary terdiri dari pasangan "value-key". "key" mengidentifikasi item, dan "value" menyimpan nilai item yang akan dipisahkan oleh tanda titik dua. Item dipisahkan dengan koma dan diapit tanda kurung kurawal. "key" tidak bisa diubah sedangkan "value" dapat berupa tipe data jenis apapun.
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