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Dictionaries are Python’s implementation of a data structure that is more generally known as an associative array. A dictionary consists of a collection of key-value pairs. Each key-value pair maps the key to its associated value. You can define a dictionary by enclosing a comma-separated list of key-value pairs in curly braces ({}).
- Dictionaries in Python
Python provides a composite data type called a dictionary,...
- Take The Quiz
Test your understanding of Python dictionaries. Python...
- Dictionaries in Python
- Creating A Python Dictionary
- Access and Delete A Key-Value Pair
- Using Try… Except
- Valid Dictionary Values
- Valid Dictionary Keys
- More Ways to Create A Python Dictionary
- Dictionary View Objects
- Merging Dictionaries
- Comparing Python Dictionaries
- Conclusion
Let’s look at how we can create and use a Python dictionary in the Python REPL: A dictionary is created by using curly braces. Inside these braces, we can add one or more key-value pairs. The pairs are separated by commas when adding more than one key-value pair. The first dictionary in our example associates keys (names like Jack and Pete) with va...
Now that you’ve seen how to initialize a dictionary, let’s see how we can add and remove entries to an already existing one:
If a requested key does not exist, an exception of type KeyErroris thrown: If you know data can be missing, e.g., when parsing input from the outside world, make sure to surround your code with a try ... except KeyError. I’ve explained this in detail in the best practices section of my article on try… except. In that article, I also explain the con...
You can put anything in a dictionary. You’re not limited to numbers or strings. In fact, you can put dictionaries and Python listsinside your dictionary and access the nested values in a very natural way: Python’s JSON decoding and encoding libraryuses this feature of Python when parsing more complex JSON documents. It creates nested trees of lists...
You can go pretty wild on your dictionary keys, too. The only requirement is that the key is hashable. Mutable types like lists, dictionaries, and sets won’t work and result in an error like: TypeError: unhashable type: ‘dict’. Besides this limitation, you can use all data types as a dictionary key, including native types like a tuple, float and in...
Depending on your data source, there are more advanced ways to initialize a dictionary that might come in handy.
Some built-in dictionary methods return a view object, offering a window on your dictionary’s keys and values. Before we start using such view objects, there’s an important concept you need to understand: values in a view object change as the content of the dictionary changes.
If you’re running Python 3.9 or later, you can use the newly introduced merging operator for dictionaries: If you’re still on a Python version between 3.5 and 3.9, you can merge two dictionaries using the following method:
If you need to compare two dictionaries, you can use a comparison operator like this: This looks and sounds trivial, but it’s not! A dictionary can contain objects of any type, after all! Consequently, Python has to walk through all the keys and values and individually compare them. You might wonder if a dictionary with the same keys and values ins...
You’ve learned what a Python dictionary is, how to create dictionaries, and how to use them. We’ve examined many practical use cases involving Python dictionaries with example code. If there’s still something missing, or you simply want to learn even more about dictionaries, you can head over to the official manual page at Python.org.
Apr 1, 2022 · We have two main methods to define a dictionary: with curly braces {} or using the dict() method. We'll create two empty dictionaries: # Create a dictionary . dictionary = {} # Curly braces method .
Oct 9, 2023 · Juliano Luiz Faccioni. learn python. ython programming. Want to master dictionaries, one of Python’s core data types? This article contains 13 Python dictionary examples with explanations and code that you can run and learn with!
Python - Dictionary. The dictionary is an unordered collection that contains key:value pairs separated by commas inside curly brackets. Dictionaries are optimized to retrieve values when the key is known. The following declares a dictionary object. Example: Dictionary.
Nov 3, 2022 · Python dictionary represents a mapping between a key and a value. In simple terms, a Python dictionary can store pairs of keys and values. Each key is linked to a specific value. Once stored in a dictionary, you can later obtain the value using just the key.
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Sep 15, 2008 · To build a dictionary from an arbitrary object, it's sufficient to use __dict__. Usually, you'll declare your methods at class level and your attributes at instance level, so __dict__ should be fine. For example: >>> class A(object): ... def __init__(self): ... self.b = 1.
