Q.Example 10.4: Create dictionaries — dict1, an empty dictionary created using curly braces; dict2, an empty dictionary created using the built-in function dict(); and dict3, the dictionary that maps names of the students to respective marks in percentage.

Dictionary Key Access

Imagine you have a physical address book. Each entry has a name (like "Ravi") and a phone number (like "[PII:phone]"). To find Ravi's number, you don't flip through every page — you look up "Ravi" directly. That name is the key, and the number is the value.

A dictionary in programming is exactly that: a collection of key-value pairs. The key is what you know; the value is what you want to retrieve. Key access is the operation of giving the dictionary a key and getting back the value tied to it.

The Intuition

Think of a real dictionary (the book). You look up a word (the key) to find its definition (the value). You never look up a definition to find the word — that would be backwards. Similarly, in a Python dictionary, you always access values by their keys, never the other way around.

The Precise Statement

In Python, dictionary key access is done using square brackets [] with the key inside, or the .get() method.

Syntax:

dictionary_name[key]

or

dictionary_name.get(key, default_value)

Example:

student = {"name": "Anjali", "age": 17, "grade": "A"}
print(student["name"])   # Output: Anjali
print(student.get("age")) # Output: 17

What Happens Under the Hood

When you write student["name"], Python:

1. Takes the key "name".
2. Computes its hash (a fixed-size number derived from the key's content).
3. Uses that hash to jump directly to the memory location where the value "Anjali" is stored.

This is why dictionary access is fast — it doesn't scan through all entries. It's a direct lookup, like using an index in a book's index rather than reading every page.