Dictionaries (dict)

Dictionaries are mutable, insertion-ordered collections of key-value pairs. Keys must be unique and immutable; values can be of any type.

Characteristics and Use Cases

• Insertion-ordered (Python 3.7+)
• Mutable: add, remove, or change key-value pairs
• Fast lookups by key
• Ideal for configuration data, JSON-like structures, and lookups

Dictionary Operations Overview

Dictionaries in Python support a variety of operations for efficient data manipulation:

• Length: Use len(my_dictionary) to get the number of key-value pairs.
• Accessing Keys, Values, and Items: Use my_dictionary.keys(), my_dictionary.values(), and my_dictionary.items() to retrieve keys, values, or key-value pairs.
• Membership Test: Check if a key exists using 'key' in my_dictionary.
• Get with Default: Use my_dictionary.get('key', default) to safely retrieve a value with a fallback.
• Setdefault: Add a key with a default value if it doesn't exist using my_dictionary.setdefault(key, default).
• Pop and Popitem: Remove a specific key with my_dictionary.pop(key) or remove an arbitrary key-value pair with my_dictionary.popitem().
• Merging: Combine dictionaries using the | operator (Python 3.9+) or update() method.
• Fromkeys: Create a new dictionary with specified keys and a default value using dict.fromkeys(keys, value).
• Clear: Remove all items from the dictionary with my_dictionary.clear().

my_dictionary = {'a': 1, 'b': 2, 'c': 3}
print(my_dictionary)

print(f"Length: {len(my_dictionary)}")

# Keys, Values, and Items
print(f"Keys: {my_dictionary.keys()}")
print(f"Values: {my_dictionary.values()}")
print(f"Items: {my_dictionary.items()}")

for item in my_dictionary.items():
    print(type(item))

for key, value in my_dictionary.items():
    print(f"- {key}: {value}")

# Membership test
print(f"'b' is in my_dictionary? {"b" in my_dictionary}")
print(f"'d' is in my_dictionary? {"d" in my_dictionary}")
print(f"1 is in my_dictionary? {1 in my_dictionary}")
print(f"1 is in values of my_dictionary? {1 in set(my_dictionary.values())}")

# Accessing elements
print("'b':", my_dictionary["b"]) # Will raise KeyError if key is not present in the dictionary
print("'b':", my_dictionary.get("b")) # Will not raise KeyError
print("'e' without default:", my_dictionary.get("e"))
print("'e' with default:", my_dictionary.get("e", -1))

my_dictionary.setdefault("d", 4)
print(my_dictionary)

# Removing elements
removed = my_dictionary.pop("a")
print(f"Removed value: {removed}")
removed = my_dictionary.popitem()
print(f"Removed value: {removed}")
removed = my_dictionary.popitem()
print(f"Removed value: {removed}")

# Merging of dictionaries
default_tags = {
    "Environment": "Production",
    "Owner": "Finance",
    "CostCenter": "10000"
}

custom_tags = {
    "CostCenter": "12345"
}

merged_tags = default_tags | custom_tags
print(merged_tags)
default_tags.update(custom_tags)
print(default_tags)

# Creating new dictionary based on a set of keys
new_dict = dict.fromkeys(['one', 'two', 'one'], 0)
print(new_dict)

new_dict.clear()
print(new_dict)

Adding and Updating Items

• server_config['port'] = 8080 # Update existing key
• server_config['environment'] = 'production' # Add new key-value pair

tags = {
    "Environment": "Production",
    "Owner": "Finance",
    "CostCenter": "10000"
}

tags["CostCenter"] = "12345"
tags["Project"] = "Python for DevOps"

print(tags)