Python - Nested Dictionaries (Complete Guide for Beginners)

 A nested dictionary in Python is a dictionary inside another dictionary. It allows you to store complex data structures in a structured and organized way.

Nested dictionaries are commonly used in real-world applications like:

• User management systems
• Student records
• Product inventories
• JSON data handling

In this tutorial, you will learn how nested dictionaries work with clear examples.

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What is a Nested Dictionary?

A nested dictionary is a dictionary that contains one or more dictionaries as values.

Example

students = {
    "student1": {"name": "John", "age": 20},
    "student2": {"name": "Alice", "age": 22}
}

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Accessing Nested Dictionary Items

You can access nested values using multiple keys.

Example

students = {
    "student1": {"name": "John", "age": 20},
    "student2": {"name": "Alice", "age": 22}
}

print(students["student1"]["name"])

Output

John

Explanation

• First key selects the main dictionary
• Second key selects the nested dictionary value

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Accessing Deeper Nested Values

Example

data = {
    "user1": {
        "profile": {
            "name": "David",
            "city": "London"
        }
    }
}

print(data["user1"]["profile"]["city"])

Output

London

---

Modifying Nested Dictionary Values

You can update values inside nested dictionaries.

Example

students = {
    "student1": {"name": "John", "age": 20}
}

students["student1"]["age"] = 21

print(students)

Output

{'student1': {'name': 'John', 'age': 21}}

---

Adding Items to Nested Dictionary

Example

students = {
    "student1": {"name": "John", "age": 20}
}

students["student1"]["grade"] = "A"

print(students)

Output

{'student1': {'name': 'John', 'age': 20, 'grade': 'A'}}

---

Adding New Nested Dictionary

Example

students = {}

students["student1"] = {
    "name": "John",
    "age": 20
}

students["student2"] = {
    "name": "Alice",
    "age": 22
}

print(students)

---

Loop Through Nested Dictionary

Example

students = {
    "student1": {"name": "John", "age": 20},
    "student2": {"name": "Alice", "age": 22}
}

for student_id, info in students.items():
    print(student_id)
    for key, value in info.items():
        print(" ", key, ":", value)

Output

student1
  name : John
  age : 20
student2
  name : Alice
  age : 22

---

Delete Items in Nested Dictionary

Example

students = {
    "student1": {"name": "John", "age": 20, "grade": "A"}
}

del students["student1"]["grade"]

print(students)

Output

{'student1': {'name': 'John', 'age': 20}}

---

Real-World Example: Student Database

school = {
    "student1": {
        "name": "John",
        "age": 20,
        "marks": {
            "math": 85,
            "science": 90
        }
    },
    "student2": {
        "name": "Alice",
        "age": 22,
        "marks": {
            "math": 88,
            "science": 92
        }
    }
}

print(school["student1"]["marks"]["science"])

Output

90

---

Real-World Example: Product Catalog

products = {
    "laptop": {
        "brand": "Dell",
        "specs": {
            "ram": "16GB",
            "storage": "512GB SSD"
        }
    },
    "phone": {
        "brand": "Samsung",
        "specs": {
            "ram": "8GB",
            "storage": "128GB"
        }
    }
}

print(products["laptop"]["specs"]["ram"])

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Advantages of Nested Dictionaries

• Organize complex data easily
• Store structured information
• Work like JSON data
• Useful in APIs and databases
• Easy data grouping

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Common Mistakes

Mistake 1: Key Error in Nested Access

❌ Wrong

print(students["student3"]["name"])

If key does not exist, Python raises an error.

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Mistake 2: Forgetting Intermediate Keys

❌ Wrong

print(students["name"])

✔ Correct way:

print(students["student1"]["name"])

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Nested Dictionary Methods Summary

Operation	Example
Access value	dict[key1][key2]
Add item	dict[key][new_key] = value
Update value	dict[key][key] = value
Delete item	del dict[key][key]
Loop	Nested for loops

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Practice Exercise 1

Print Alice's age.

students = {
    "student1": {"name": "John", "age": 20},
    "student2": {"name": "Alice", "age": 22}
}

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Practice Exercise 2

Add a new subject score inside marks.

student = {
    "name": "Tom",
    "marks": {"math": 80}
}

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Conclusion

Nested dictionaries are powerful tools in Python for handling complex and structured data.

You learned:

• How to create nested dictionaries
• How to access and modify data
• How to loop through nested structures
• Real-world use cases like students and products

Mastering nested dictionaries is essential for working with APIs, JSON, databases, and real-world applications.