Question

Suppose a dictionary named inventory exists. What does the following statement do? del inventory [654]

Short answer

Answer: The statement "del inventory[654]" deletes the item with key '654' from the 'inventory' dictionary if it exists. If the key '654' does not exist in the dictionary, a KeyError will be raised.

Step-by-step solution

Understanding Dictionaries and 'del' operation

In Python, a dictionary is a mutable, unordered collection of key-value pairs where each key must be unique. The 'del' operation in Python is used to delete an item from a dictionary by using its key. Here, the 'inventory' is a dictionary and the statement is trying to delete an item with a key of 654.

Analyzing the Statement: del inventory[654]

This statement is performing a 'del' operation on the 'inventory' dictionary. It will search for an item with a key of '654' in the dictionary and will delete that item, if it exists.

Possible Outcomes

1. If the key '654' exists in the 'inventory' dictionary, the item with the key '654' will be deleted from the dictionary. 2. If the key '654' does not exist in the 'inventory' dictionary, Python will raise a KeyError indicating that the given key is not present in the dictionary.

Key concepts

Python dictionaries

Python dictionaries are fundamental data structures that store data in a key-value pair format, making data retrieval fast and efficient.

Imagine a Python dictionary like a real-life dictionary, where you look up a word (the key) to find its definition (the value). Every key is unique, and it points to a value which can be of any data type. Dictionaries in Python are mutable, meaning you can add, remove, or change items after the dictionary has been created.

To create a dictionary, you use curly braces ({}), with key-value pairs separated by colons, and pairs separated by commas. Here's an example of a simple dictionary:

{'apple': 'green', 'banana': 'yellow', 'cherry': 'red'}

You can access a value by referencing its key, as dictionaries do not maintain any order for their elements. For instance, fruit_colors['apple'] would return 'green'.

Dictionaries provide an efficient way to associate keys with values, making them incredibly powerful for a variety of programming tasks where quick data lookup is essential.

del operation in Python

The del operation in Python is a versatile statement used for deleting objects. When applied to dictionaries, it deletes an item by key.

For example, if we have a dictionary named inventory, and we want to remove the item with key 654, we would write:

del inventory[654]

This operation looks for the key 654 in the inventory dictionary, and if it finds it, removes the key-value pair from the dictionary. It's important to ensure that the key you wish to delete actually exists within the dictionary to prevent errors in your program.

Using del is straightforward and effective for cases where you know the exact key and want to remove its corresponding value. However, if you attempt to delete a non-existent key, Python will raise an exception. These aspects make the del operation a powerful tool for dictionary manipulation in Python.

KeyError exception

A KeyError exception in Python is raised when you attempt to access or delete an item in a dictionary using a key that does not exist in the dictionary.

This error is Python's way of telling you that it cannot find the specified key. For instance, if we have a dictionary:

{'apple': 5, 'banana': 8, 'cherry': 3}

and we try to delete an item with a non-existent key, like so:

del fruit['orange']

Python will raise a KeyError because 'orange' is not a key in the fruit dictionary.

One way to avoid a KeyError is to first check if the key exists by using the in operator:

if 'orange' in fruit:
    del fruit['orange']
else:
    print('Key not found')

This check ensures you do not attempt to delete a key that isn't present, which enhances the robustness of your code. Remember, handling exceptions like KeyError is a good practice in programming, especially when working with operations that can potentially cause these exceptions.