Appending a dictionary to a list in Python

In Python, dictionaries store key-value pairs while lists store multiple values in sequence. Appending dictionaries to lists is useful for collecting structured data, such as storing multiple records or configurations in a single container.

Basic List and Dictionary Overview

A list is an ordered collection of items enclosed in square brackets []. A dictionary is an ordered collection of key-value pairs enclosed in curly braces {}.

# List example
sample_list = ["Apple", "Banana", "Cherry"]
print("List:", sample_list)

# Dictionary example
student = {"name": "John", "age": 25, "grade": "A"}
print("Dictionary:", student)

List: ['Apple', 'Banana', 'Cherry']
Dictionary: {'name': 'John', 'age': 25, 'grade': 'A'}

Using append() Method

The append() method adds a dictionary as a single element to the end of a list ?

# Create a list with existing elements
students = ["Math", "Science"]

# Create a dictionary
student_info = {"name": "Alice", "age": 20, "subject": "Physics"}

# Append dictionary to list
students.append(student_info)
print(students)

['Math', 'Science', {'name': 'Alice', 'age': 20, 'subject': 'Physics'}]

Using append() with copy()

When you need to avoid reference issues, use copy() to create a shallow copy before appending ?

import copy

# Create list and dictionary
data_list = []
original_dict = {"city": "Delhi", "population": 30000000}

# Append copy to avoid reference issues
data_list.append(original_dict.copy())

# Modify original dictionary
original_dict["population"] = 32000000

print("List:", data_list)
print("Original dict:", original_dict)

List: [{'city': 'Delhi', 'population': 30000000}]
Original dict: {'city': 'Delhi', 'population': 32000000}

Using append() with deepcopy()

For dictionaries containing nested objects, use deepcopy() to create a complete independent copy ?

import copy

# List to store records
records = []

# Dictionary with nested structure
employee = {
    "name": "Bob", 
    "details": {"department": "IT", "salary": 75000}
}

# Deep copy before appending
records.append(copy.deepcopy(employee))

# Modify original nested dictionary
employee["details"]["salary"] = 80000

print("Records:", records)
print("Original employee:", employee)

Records: [{'name': 'Bob', 'details': {'department': 'IT', 'salary': 75000}}]
Original employee: {'name': 'Bob', 'details': {'department': 'IT', 'salary': 80000}}

Appending Multiple Dictionaries

You can append multiple dictionaries to build a collection of related records ?

# Create empty list for storing multiple records
inventory = []

# Create multiple dictionaries
item1 = {"product": "Laptop", "price": 50000, "stock": 25}
item2 = {"product": "Mouse", "price": 500, "stock": 100}
item3 = {"product": "Keyboard", "price": 1500, "stock": 75}

# Append all dictionaries
inventory.append(item1)
inventory.append(item2)
inventory.append(item3)

print("Inventory:")
for item in inventory:
    print(f"- {item['product']}: ?{item['price']} (Stock: {item['stock']})")

Inventory:
- Laptop: ?50000 (Stock: 25)
- Mouse: ?500 (Stock: 100)
- Keyboard: ?1500 (Stock: 75)

Comparison of Methods

Conclusion

Use append() for basic dictionary addition to lists. Choose copy() or deepcopy() when you need independent copies to avoid unintended modifications.