A key is the object used to look up a corresponding value in a Python dictionary. Each dictionary entry is a key-value pair: the key appears before the colon, and its value appears after it. For example, a grocery dictionary can use item names as keys and quantities as values. section 27.1
Keep these key rules in mind:
- Keys must be immutable objects, so their contents cannot change while the dictionary uses them. section 27.2
- Every key must be unique. Assigning a new value to an existing key overwrites the previous value instead of creating another entry. section 27.2
- Values may be mutable or immutable, and a value can contain several objects inside one tuple or list. section 27.1 section 27.6
- A key can retrieve its value directly, or you can inspect all keys with keys() and loop through them. section 27.4
Grocery quantities
grocery = {"milk": 1, "eggs": 12, "bread": 2} print(grocery["eggs"]) Here, "eggs" is the key, and 12 is its value. The square brackets ask the dictionary to retrieve the value associated with that key. Replacing it with grocery["eggs"] = 18 changes the existing entry. section 27.1 section 27.2
grocery = {"milk": 1, "eggs": 12, "bread": 2}
View the compact dictionary example showing keys on the left of each colon and their corresponding values on the right. section 27.1
