Python Dictionaries – Storing Key-Value Pairs

Dictionaries are Python’s way of storing data as key-value pairs. Think of them like a real dictionary where you look up a word (key) to find its definition (value).

Creating Dictionaries

Use curly braces to create dictionaries:

student = {
    "name": "Alice",
    "age": 20,
    "major": "Computer Science"
}

# Empty dictionary
empty_dict = {}

Accessing Dictionary Values

Use keys to access their corresponding values:

print(student["name"])     # Alice
print(student["age"])      # 20

# Safe access with get()
print(student.get("grade", "Not found"))  # Not found

Modifying Dictionaries

Add new key-value pairs or update existing ones:

# Add new items
student["grade"] = "A"
student["year"] = "Junior"

# Update existing items
student["age"] = 21

# Remove items
del student["year"]
removed_grade = student.pop("grade")

Dictionary Methods

Useful methods for working with dictionaries:

# Get all keys, values, or items
print(student.keys())    # dict_keys(['name', 'age', 'major'])
print(student.values())  # dict_values(['Alice', 21, 'Computer Science'])
print(student.items())   # dict_items([('name', 'Alice'), ...])

Looping Through Dictionaries

# Loop through keys
for key in student:
    print(f"{key}: {student[key]}")

# Loop through key-value pairs
for key, value in student.items():
    print(f"{key}: {value}")

# Loop through values only
for value in student.values():
    print(value)

Practical Example

# Count word occurrences
text = "hello world hello python"
word_count = {}

for word in text.split():
    if word in word_count:
        word_count[word] += 1
    else:
        word_count[word] = 1

print(word_count)  # {'hello': 2, 'world': 1, 'python': 1}

Dictionaries are perfect for storing related information and creating lookups in your programs.