Summary  
This chapter covers how to insert elements at specific positions in a list using the list.insert(index, element) method with zero-based indexing.  

General domain of usage  
Travel itinerary planning

What if you want to add an item not at the end of the list, but at a specific position. For this purpose, you can use the `insert()` method. The syntax for the `insert()` method is:

``` python
list.insert(index, element)
```
- `index`: the position in the list where you want to add the new element. Remember, Python uses **zero-based** indexing;
- `element`: the item you want to insert into the list.

Imagine planning a trip and having a list of cities you want to visit.

travel_wishlist = ["Paris", "Oslo", "Kyoto", "Sydney"]

print(travel_wishlist)  # Output: ['Paris', 'Oslo', 'Kyoto', 'Sydney']

However, your plans change, and you decide to adjust the order of destinations.
Now, you want to prioritize "Chicago" as the first destination.

travel_wishlist = ["Paris", "Oslo", "Kyoto", "Sydney"]

# Adding "Rome" as the first destination
travel_wishlist.insert(0, "Chicago")
print(travel_wishlist)  # Output: ['Chicago', 'Paris', 'Oslo', 'Kyoto', 'Sydney']

After this, "Chicago" takes the `0` index. It's now at the top, and the rest of the items have shifted down. So, we now have 5 items:





With the `insert()` function, you can add **only one** item at once.

Note

import unittest
from contextlib import redirect_stdout
import io
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_travel_wishlist_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'travel_wishlist'),
            "The `travel_wishlist` list is declared.",
            "Expected `travel_wishlist` to be declared."
        )

    def test_cities_prioritized_correctly(self):
        import user_code
        expected_list = ["London", "Paris", "Budapest", "Oslo", "Kyoto", "Sydney"]
        _dynamic_test(
            self,
            user_code.travel_wishlist == expected_list,
            f"The cities were prioritized correctly: {user_code.travel_wishlist}.",
            f"Expected travel_wishlist to be {expected_list}, but got {user_code.travel_wishlist}."
        )

    def test_insert_method_used(self):
        with open('user_code.py', 'r') as file:
            user_code_source = file.read()
        
        _dynamic_test(
            self,
            ".insert(" in user_code_source,
            "The `insert` method is used to prioritize cities.",
            "Expected the `insert` method to be used to prioritize cities."
        )

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.

Placing Elements at Specific Positions in Python

解答