Defining the Python Dictionary: Key-Value Mapping

In Python, the Dictionary is a flexible, fundamental data type used for storing data in a descriptive, rather than positional, manner. Unlike sequences like Lists or Tuples, a dictionary is an unordered collection where data is organized using unique names called keys instead of numerical indices. This structure enables incredibly fast data lookup.

1. The Core Structure: Key-Value Pairs

Data is stored as pairs, where a unique Key maps directly to a Value. This design mimics an optimized hash map, ensuring extremely fast retrieval. Keys must be unique and immutable (typically strings or numbers), while Values can be any data type.

{"student_id": 101, "name": "Alex", "grade": 88.5}

2. Dictionary Syntax and Properties

Dictionaries are defined using curly braces {}.
The colon : separates the Key from its corresponding Value (Key:Value).
Dictionaries are mutable, meaning keys and values can be dynamically added, deleted, or modified after creation.

💡 Indexing vs. Key Lookup

Dictionaries do not support numerical indexing (like [0] or [1]). Data must be retrieved using the specific key name provided during creation (e.g., dictionary["name"]).

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Question 1

How are keys and values separated within a Python dictionary?

Comma (,)

Semicolon (;)

Colon (:)

Dash (-)

Question 2

Which symbol is used to define a Python dictionary?

Square Brackets [ ]

Parentheses ( )

Curly Braces { }

Angle Brackets < >

Question 3

If you try to access data in the dictionary settings using settings[0], what will happen?

It will return the first item.

It will return the item associated with the key '0'.

A Key Error will likely occur if the key '0' does not exist.

Nothing, dictionaries are immutable.

Configuration Manager

Practice modeling configuration data.

You are designing a configuration object for a new application feature. The configuration requires three settings:

max_users set to 50
debug_mode set to True
log_level set to 'INFO'

Your task is to:

Create a dictionary named app_config containing these three key-value pairs.
Print the log_level value.
Change the max_users value to 100.

Step 1

How do you create the app_config dictionary?

Solution:
Use curly braces and separate keys and values with colons.

Code: app_config = {"max_users": 50, "debug_mode": True, "log_level": "INFO"}

Step 2

How do you retrieve the log_level?

Solution:
Access the dictionary using the key in square brackets.

Code: print(app_config["log_level"])

Step 3

How do you update max_users?

Solution:
Assign a new value to the existing key.

Code: app_config["max_users"] = 100