Modifying Dictionary Items in Python
Introduction
A dictionary in Python is an unordered collection of key-value pairs. Dictionaries are very useful for storing associative data where each key is unique. You can easily modify dictionary items by changing the values associated with keys or updating the dictionary with new key-value pairs.
Changing Dictionary Values
To change the value associated with a specific key in a dictionary, you access the key and assign a new value to it.
Example 1: Changing a Value
# Creating a dictionary
my_dict = {
'name': 'Alice',
'age': 30,
'city': 'Paris'
}
# Displaying the dictionary before modification
print("Before modification:", my_dict)
# Changing the value associated with the key 'age'
my_dict['age'] = 31
# Displaying the dictionary after modification
print("After modification:", my_dict)
# Output:
# Before modification: {'name': 'Alice', 'age': 30, 'city': 'Paris'}
# After modification: {'name': 'Alice', 'age': 31, 'city': 'Paris'}
In this example, we changed Alice’s age from 30 to 31.
Updating a Dictionary
There are several ways to update a dictionary:
- Adding New Key-Value Pairs
- Using the update() Method
Adding New Key-Value Pairs
You can add new key-value pairs to a dictionary using a syntax similar to changing values. If the key does not already exist, it will be added with the specified value.
Example 2: Adding a New Key
# Creating a dictionary
my_dict = {
'name': 'Bob',
'age': 25
}
# Displaying the dictionary before addition
print("Before addition:", my_dict)
# Adding a new key-value pair
my_dict['city'] = 'London'
# Displaying the dictionary after addition
print("After addition:", my_dict)
# Output:
# Before addition: {'name': 'Bob', 'age': 25}
# After addition: {'name': 'Bob', 'age': 25, 'city': 'London'}
Using the update() Method
The update() method allows you to update a dictionary with key-value pairs from another dictionary or an iterable of key-value pairs.
Example 3: Updating with Another Dictionary
# Initial dictionary
my_dict = {
'name': 'Charlie',
'age': 28
}
# Dictionary with information to add
update_dict = {
'city': 'Berlin',
'profession': 'Developer'
}
# Updating the initial dictionary
my_dict.update(update_dict)
# Displaying the dictionary after update
print("After update:", my_dict)
# Output:
# After update: {'name': 'Charlie', 'age': 28, 'city': 'Berlin', 'profession': 'Developer'}
Example 4: Updating with Key-Value Pairs
# Initial dictionary
my_dict = {
'name': 'David',
'age': 40
}
# Updating with key-value pairs
my_dict.update({'city': 'Madrid', 'age': 41})
# Displaying the dictionary after update
print("After update:", my_dict)
# Output:
# After update: {'name': 'David', 'age': 41, 'city': 'Madrid'}
In this example, we updated the age and added the city to the dictionary.
Conclusion
Modifying dictionary items in Python is straightforward. You can change the values associated with existing keys, add new key-value pairs, or update the dictionary with other dictionaries or key-value pairs. These operations are essential for effectively managing and manipulating data using dictionaries.