Glossary

10.2 Dictionary creation

2 min read•june 24, 2024

Dictionaries in Python are versatile data structures for storing . They offer flexible creation methods, from to the function, allowing easy initialization with various data types.

Advanced operations enhance their utility. Comprehensions, methods, and lookup techniques make dictionaries powerful tools for organizing and accessing data efficiently in Python programs.

Dictionary Creation in Python

Dictionary creation with curly braces

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  • Create dictionaries using curly braces with initial key-value pairs
    • Define unique keys and their corresponding values separated by colons
      • (
        my_dict = {'name': 'John', 'age': 25, 'city': 'New York'}
        )
  • Keys must be unique and objects (strings, numbers, tuples)
    • Duplicate keys result in the last assigned value being used
  • Values can be any data type (mutable or ) and can be duplicated
    • (
      {'a': 1, 'b': [2, 3], 'c': 'hello', 'd': (4, 5)}
      )
    • can be created by using dictionaries as values

Dict() function for data conversion

  • Convert other data types into dictionaries using the dict() function
    • Lists of tuples can be converted to dictionaries
      • Each tuple should contain exactly two elements (key, value)
        • (
          dict([('name', 'John'), ('age', 25), ('city', 'New York')]
          )
    • Keyword arguments can create dictionaries
      • Argument names become keys and argument values become values
        • (
          dict(name='John', age=25, city='New York')
          )
  • Keyword arguments used with dict() must be valid Python identifiers
    • No spaces or special characters, except underscore (_)

Methods of dictionary initialization

  • Create empty dictionaries using curly braces or dict() without arguments
    • Curly braces: 
      my_dict = {}
    • Dict() function: 
      my_dict = dict()
  • Initialize dictionaries with key-value pairs using curly braces or dict()
    • Curly braces: 
      my_dict = {'key1': value1, 'key2': value2}
    • Dict() with keyword arguments: 
      my_dict = dict(key1=value1, key2=value2)
    • Dict() with list of tuples: 
      my_dict = dict([('key1', value1), ('key2', value2)])
  • Choose the appropriate dictionary creation method based on the use case and initial data format
    • Curly braces for simple key-value pairs
    • Dict() for converting other data types or using keyword arguments

Advanced Dictionary Operations

  • allows for concise creation of dictionaries based on existing iterables
  • Iteration over dictionaries can be done using methods like .keys(), .values(), or .items()
  • is performed using square brackets or the .get() method, which can provide
    • Example: 
      my_dict.get('key', default_value)

Key Terms to Review (15)

{}: The curly braces, {}, are a pair of punctuation marks used in various programming languages, including Python, to enclose and define a dictionary or a set. A dictionary is a collection of key-value pairs, where the keys are unique identifiers, and the values can be any data type. The curly braces are used to create and represent a dictionary in Python.
Curly Braces: Curly braces, also known as curly brackets, are a pair of symbols { } used in programming languages, including Python, to enclose and define various programming constructs such as blocks of code, dictionaries, and sets. They play a crucial role in the syntax and structure of these programming elements.
Default Values: Default values refer to the predetermined values that are assigned to parameters or variables when they are not explicitly provided. These default values serve as fallback options, ensuring that the code can still function even when certain inputs are missing.
Dict(): dict() is a built-in function in Python that creates a new dictionary object. Dictionaries are data structures that store key-value pairs, allowing for efficient storage and retrieval of data.
Dictionary: A dictionary in Python is a collection of key-value pairs where each key is unique. It allows for efficient data retrieval based on the keys.
Dictionary: A dictionary in Python is an unordered collection of key-value pairs, where each key is unique and is associated with a corresponding value. Dictionaries provide a flexible and efficient way to store and retrieve data, making them a fundamental data structure in the language.
Dictionary comprehension: Dictionary comprehension is a concise way to create dictionaries in Python using a single line of code, allowing for the transformation and filtering of data in a readable manner. This technique combines looping and conditionals into one expression, making it efficient and clean, especially when generating dictionaries from existing iterable data like lists or other dictionaries.
Hashable: Hashable is a fundamental concept in Python that refers to the ability of an object to be used as a key in a dictionary or as an element in a set. Hashable objects have a stable hash value, which means that their hash value does not change during the lifetime of the object, allowing them to be used in hash-based data structures like dictionaries and sets.
Immutable: Immutable means that an object cannot be altered after it is created. In Python, strings and tuples are examples of immutable objects.
Immutable: Immutable refers to an object or variable that cannot be changed or modified once it has been created. This concept is fundamental in programming, as it affects the way data is stored, manipulated, and accessed across various programming topics.
Iteration: Iteration is the process of repeating a set of instructions or operations multiple times in a computer program or algorithm. It is a fundamental concept in programming that allows for the execution of a block of code repeatedly until a specific condition is met.
Key Lookup: Key lookup refers to the process of retrieving the value associated with a specific key in a dictionary or other data structure that uses a key-value pair organization. It is a fundamental operation in the context of dictionary creation and manipulation.
Key-Value Pairs: Key-value pairs are the fundamental building blocks of dictionaries in Python. They consist of a unique key, which acts as an identifier, and an associated value that represents the data stored under that key.
Nested dictionaries: A nested dictionary is a dictionary within another dictionary. It allows for hierarchical data structures where values can themselves be dictionaries.
Nested Dictionaries: Nested dictionaries, also known as dictionaries within dictionaries, are a data structure in Python where the values of a dictionary can be other dictionaries. This allows for the creation of complex, hierarchical data structures that can represent more intricate relationships and information.
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