Summary  
Demonstrates how to retrieve values from a Python dictionary by key, assign them to a variable, and printing the result.

General domain of usage  
Library catalog management

Let's build a dictionary to represent a book in a library:

book = {"title": "Pride and Prejudice", "author": "Jane Austen", "year": 1813}
print(book)

This dictionary includes three key-value pairs:

In a dictionary, you can retrieve an item by referencing its key. Here's an example of accessing the publication year of the book:

book = {"title": "Pride and Prejudice", "author": "Jane Austen", "year": 1813}

publication_year = book["year"]
print(publication_year)  # Output: 1813

In the code provided:

- Python searches for the key `"year"` in the book dictionary;
- It retrieves the value associated with the key (`1813`) and assigns it to the variable `publication_year`.

The value is then printed, demonstrating how keys allow quick and specific access to dictionary values.

import unittest
import importlib

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

class TestUserCode(unittest.TestCase):

    def test_authors_books_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'authors_books'),
            "The `authors_books` dictionary is declared.",
            "Expected `authors_books` dictionary to be declared."
        )

    def test_authors_books_is_dict(self):
        import user_code
        _dynamic_test(
            self,
            isinstance(user_code.authors_books, dict),
            "The `authors_books` is of type `dict`.",
            "Expected `authors_books` to be of type `dict`."
        )

    def test_kings_books_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'kings_books'),
            "The `kings_books` list is declared.",
            "Expected `kings_books` to be declared."
        )

    def test_shekspeares_books_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'shakspeares_books'),
            "The `shakspeares_books` list is declared.",
            "Expected `shakspeares_books` to be declared."
        )

    def test_kings_books_is_list(self):
        import user_code
        _dynamic_test(
            self,
            isinstance(user_code.kings_books, list),
            "The `kings_books` is of type `list`.",
            "Expected `kings_books` to be of type `list`."
        )

    def test_shekspeares_books_is_list(self):
        import user_code
        _dynamic_test(
            self,
            isinstance(user_code.shakspeares_books, list),
            "The `shakspeares_books` is of type `list`.",
            "Expected `shakspeares_books` to be of type `list`."
        )

    def test_kings_books_correct_values(self):
        import user_code
        expected_books = ['It', 'The Shining', 'Carrie', 'Misery']
        _dynamic_test(
            self,
            user_code.kings_books == expected_books,
            "The `kings_books` list contains the correct books.",
            f"Expected `kings_books` to be {expected_books}, but got {user_code.kings_books}."
        )

    def test_shekspeares_books_correct_values(self):
        import user_code
        expected_books = ['Hamlet', 'Macbeth', 'Romeo and Juliet', 'Othello']
        _dynamic_test(
            self,
            user_code.shakspeares_books == expected_books,
            "The `shakspeares_books` list contains the correct books.",
            f"Expected `shekspeares_books` to be {expected_books}, but got {user_code.shakspeares_books}."
        )

    def test_books_are_retrieved_using_dict_indexing(self):
        with open('user_code.py', 'r') as file:
            user_code_source = file.read()
        
        _dynamic_test(
            self,
            "'Stephen King'" in user_code_source and "'William Shakespeare'" in user_code_source,
            "The books are retrieved using dictionary indexing.",
            "Expected the books to be retrieved using dictionary indexing."
        )

if __name__ == '__main__':
    unittest.main()


test_main.py

Explore the fundamental data structures of the Python programming language, including lists, dictionaries, tuples, and sets, and learn how to apply them effectively to solve real-world programming challenges.

What is a list? A list is an ordered collection that can be modified. It also allows for duplicate elements.

Accessing Dictionary Values in Python

解答