Python Dictionaries

What is a Python Dictionary?

A dictionary in Python is a collection of key-value pairs. Think of it as a real-world dictionary, where you look up a word (key) to find its meaning (value). A dictionary allows you to store and retrieve data efficiently.

Key Features of a Python Dictionary:

• Unordered: The items do not have a specific order.
• Mutable: You can change the content (add, remove, update items).
• Indexed by keys: Instead of using numbers (like lists or arrays), you use keys.

Structure of a Dictionary

A dictionary is written using curly braces {}, with each key-value pair separated by a colon (:). Here’s the syntax:

my_dict = {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
}

1. Creating a Dictionary

Let’s start by creating a simple dictionary:

# Create a dictionary
person = {
    "name": "John",
    "age": 25,
    "city": "New York"
}

print(person)

Output:

{'name': 'John', 'age': 25, 'city': 'New York'}

2. Accessing Values in a Dictionary

You can access values in a dictionary by referencing the key. For example, to get the name of the person:

print(person["name"])  # Output: John

Explanation: The code person["name"] retrieves the value associated with the key "name", which is "John".

3. Adding Items to a Dictionary

You can add new key-value pairs to a dictionary like this:

# Add a new key-value pair
person["job"] = "Software Developer"

print(person)

Output:

{'name': 'John', 'age': 25, 'city': 'New York', 'job': 'Software Developer'}

4. Changing Values in a Dictionary

You can update the value of an existing key by referencing the key and assigning a new value:

# Change the value of an existing key
person["age"] = 26

print(person)

Output:

{'name': 'John', 'age': 26, 'city': 'New York', 'job': 'Software Developer'}

5. Removing Items from a Dictionary

You can remove items from a dictionary using the del keyword or the pop() method.

# Remove an item using del
del person["city"]

print(person)

Output:

{'name': 'John', 'age': 26, 'job': 'Software Developer'}

Alternatively, you can use pop():

# Remove an item using pop()
removed_value = person.pop("job")

print(person)
print("Removed Value:", removed_value)

Output:

{'name': 'John', 'age': 26}
Removed Value: Software Developer

6. Looping Through a Dictionary

You can loop through a dictionary to access each key and value. Here’s how:

# Loop through dictionary keys and values
for key, value in person.items():
    print(key, ":", value)

Output:

name : John
age : 26

7. Checking If a Key Exists in a Dictionary

To check if a specific key is in the dictionary, you can use the in keyword:

# Check if a key exists
if "name" in person:
    print("The key 'name' is in the dictionary.")

Output:

The key 'name' is in the dictionary.

8. Dictionary Methods

Here are some useful methods you can use with dictionaries:

• keys(): Returns a list of keys in the dictionary.
• values(): Returns a list of values in the dictionary.
• items(): Returns a list of tuples, where each tuple is a key-value pair.

print(person.keys())   # Output: dict_keys(['name', 'age'])
print(person.values()) # Output: dict_values(['John', 26])
print(person.items())  # Output: dict_items([('name', 'John'), ('age', 26)])

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Displaying Code and Output on WordPress

To display Python code and its output on a WordPress page or post, you can follow these steps:

Step 1: Install a Code Syntax Highlighter Plugin

First, install a plugin like “SyntaxHighlighter Evolved” or “Crayon Syntax Highlighter” to format and display your code in a readable manner.

Step 2: Embed Python Code in WordPress

Once the plugin is installed, you can embed your Python code in a post or page like this:

[code language="python"]
# Create a dictionary
person = {
    "name": "John",
    "age": 25,
    "city": "New York"
}

# Print the dictionary
print(person)
[/code]

Step 3: Add Sample Output

You can add the sample output below the code block in the post like this:

<p><strong>Output:</strong></p>
<pre>
{'name': 'John', 'age': 25, 'city': 'New York'}
</pre>