How to Replace values in a Dictionary in Python

# Table of Contents

1. Replace values in a dictionary in Python
2. Replace values in a dictionary using dictionary unpacking
3. Replace values in a dictionary using a for loop
4. Replace values in a dictionary using the dictionary merge operator
5. Replace values in a dictionary based on another dictionary
6. Replace values in a dictionary using a dict comprehension

# Replace values in a dictionary in Python

Use the dict.update() method to replace values in a dictionary.

The dict.update() method updates the dictionary with the key-value pairs from the provided value.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}


my_dict.update(
    {'name': 'borislav',
     'site': 'bobbyhadz.com'
    }
)

# 👇️ {'name': 'borislav', 'site': 'bobbyhadz.com', 'id': 1, 'topic': 'Python'}
print(my_dict)

We used the dict.update() method to replace values in a dictionary.

The dict.update() method updates the dictionary with the key-value pairs from the provided value.

The method overrides the dictionary's existing keys and returns None.

# Passing keyword arguments to the dict.update() method

You can also pass keyword arguments to the dict.update() method.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}


my_dict.update(
    [
        ('name', 'borislav'),
        ('site', 'bobbyhadz.com')
    ]
)

# 👇️ {'name': 'borislav', 'site': 'bobbyhadz.com', 'id': 1, 'topic': 'Python'}
print(my_dict)

Alternatively, you can use the dictionary unpacking ** operator.

# Replace values in a dictionary using dictionary unpacking

This is a three-step process:

1. Use the dictionary unpacking operator to unpack the key-value pairs into a new dictionary.
2. Specify the keys with the updated values.
3. The new values will override the values of the existing keys.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

my_dict = {
    **my_dict,
    'name': 'borislav',
    'site': 'bobbyhadz.com'
}

# 👇️ {'name': 'borislav', 'site': 'bobbyhadz.com', 'id': 1, 'topic': 'Python'}
print(my_dict)

We used the dictionary unpacking ** operator to unpack the key-value pairs of the dictionary into a new dictionary.

The name and site keys override the values of the existing keys with the same names.

Alternatively, you can use a for loop.

# Replace values in a dictionary using a for loop

This is a three-step process:

1. Use a for loop to iterate over the dictionary's items.
2. Check if each value should be updated.
3. Replace the matching values.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

for key, value in my_dict.items():
    if value == 'default':
        if key == 'name':
            my_dict[key] = 'borislav'
        elif key == 'site':
            my_dict[key] = 'bobbyhadz.com'


# 👇️ {'name': 'borislav', 'site': 'bobbyhadz.com', 'id': 1, 'topic': 'Python'}
print(my_dict)

The dict.items() method returns a new view of the dictionary's items ((key, value) pairs).

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

# 👇️ dict_items([('name', 'default'), ('site', 'default'), ('id', 1), ('topic', 'Python')])
print(my_dict.items())

On each iteration, we check if the current value should be replaced and replace the matching values.

# Replace values in a dictionary using the dictionary merge operator

You can also use the dictionary merge operator to replace values in a dictionary.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

my_dict = my_dict | {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com'
}

# {'name': 'bobby hadz', 'site': 'bobbyhadz.com',
#  'id': 1, 'topic': 'Python'}
print(my_dict)

The dictionary merge (|) operator is available starting with Python version 3.9.

You can check your version of Python by running the following command.

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python --version

The dictionary merge (|) operator creates a new dictionary.

The is also a dictionary update (|=) operator that is used for assignment.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

my_dict |= {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com'
}

# {'name': 'bobby hadz', 'site': 'bobbyhadz.com',
#  'id': 1, 'topic': 'Python'}
print(my_dict)

Make sure your version of Python is 3.9 or more recent to be able to run the code sample.

# Replace values in a dictionary based on another dictionary

You can also use a for loop to replace the values in a dictionary based on another dictionary.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

another_dict = {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com'
}

for key, value in another_dict.items():
    my_dict[key] = value

# 👇️ {'name': 'bobby hadz', 'site': 'bobbyhadz.com',
#  'id': 1, 'topic': 'Python'}
print(my_dict)

We used a for loop to iterate over the items of the second dictionary.

On each iteration, we replace the key-value pair of the first dictionary.

You can also check for the existence of the keys in the first dictionary.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

another_dict = {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com',
    'abc': 'xyz',
    'one': 'two',
}

for key, value in another_dict.items():
    if key in my_dict:
        my_dict[key] = value

# 👇️ {'name': 'bobby hadz', 'site': 'bobbyhadz.com',
#  'id': 1, 'topic': 'Python'}
print(my_dict)

On each iteration, we use the in operator to check if the current key is contained in the dictionary.

The keys are only replaced if they exist in the first dictionary.

# Replace values in a dictionary using a dict comprehension

You can also use a dict comprehension to replace values in a dictionary.

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my_dict = {
    'name': 'default',
    'site': 'default',
    'id': 1,
    'topic': 'Python'
}

another_dict = {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com',
    'abc': 'xyz',
    'one': 'two',
}

my_dict = {
    key: another_dict.get(key, value)
    for key, value in my_dict.items()
}

# {'name': 'bobby hadz', 'site': 'bobbyhadz.com',
# 'id': 1, 'topic': 'Python'}
print(my_dict)

We used a dict comprehension to iterate over the dictionary's items.

Dict comprehensions are very similar to list comprehensions.

They perform some operation for every key-value pair in the dictionary or select a subset of key-value pairs that meet a condition.

On each iteration, we use the dict.get() method to get the value of the key in the second dictionary.

We specified the current value as a fallback in case the key doesn't exist in the second dictionary.

The dict.get method returns the value for the given key if the key is in the dictionary, otherwise a default value is returned.

The method takes the following 2 parameters:

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another_dict = {
    'name': 'bobby hadz',
    'site': 'bobbyhadz.com',
    'abc': 'xyz',
    'one': 'two',
}

print(another_dict.get('id'))  # 👉️ None
print(another_dict.get('topic'))  # 👉️ None

print(another_dict.get('name'))  # 👉️ bobby hadz

If a value for the default parameter is not provided, it defaults to None, so the get() method never raises a KeyError.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Get multiple values from a Dictionary in Python
• Get random Key and Value from a Dictionary in Python
• Join the Keys or Values of Dictionary into String in Python
• Multiply the Values in a Dictionary in Python
• Print specific key-value pairs of a dictionary in Python
• How to set all Dictionary values to 0 in Python
• How to merge two JSON objects in Python
• How to destructure Dictionaries and Lists in Python