7.5.3. Manipulating Items

In this section, we'll see some ways of manipulating the items of a dictionary data structure.

Setting Key Values

The most basic way of adding an element to a dictionary is by setting the key to its value.

CodeOutput

data = {}
data['name'] = 'John'
data['age'] = 25

print(data)

{'name': 'John', 'age': 25}

Note that if the key already exists in the dictionary, its value is updated with the new one.

CodeOutput

data = {}

data['name'] = 'John'
data['age'] = 25
print(data)

data['name'] = 'Alex'
print(data)

{'name': 'John', 'age': 25}
{'name': 'Alex', 'age': 25}

Updating dictionary

A dictionary can be updated with the new one using the dict.update() method. It takes another dictionary which is merged with original one.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

data.update({'gender': 'male', 'role': 'Manager'})
print(data)

{'name': 'John', 'age': 25, 'gender': 'male', 'role': 'Manager'}

If a key in new dictionary already exists in original one, its value in original is updated with new one.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

data.update({'gender': 'male', 'name': 'Alex'})
print(data)

{'name': 'Alex', 'age': 25, 'gender': 'male'}

dict.update() can also take any iterable with key value pairs (a sequence with two values, first one being the key and second representing the value).

For example, we're passing a list of two key-value pairs here:

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

data.update([('gender', 'male'), ('role', 'Manager')])
print(data)

{'name': 'John', 'age': 25, 'gender': 'male', 'role': 'Manager'}

Deleting Items (del Keyword)

The del keyword can be used to remove a key from the dictionary.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

del data['name']
print(data)

{'age': 25}

The key must exist. If not, a KeyError is raised.

Deleting Items (Methods)

dict.pop() removes an item from the dictionary by its key name and returns the value.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

print(data.pop('age'))
print(data)

25
{'name': 'John'}

If the key does not exist, it raises a KeyError unless a default value is provided as second parameter.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

print(data.pop('gender', 'male'))
print(data)

male
{'name': 'John', 'age': 25}

Since gender key didn't exist, the default value provided as second parameter was returned instead of raising KeyError.

There is also a dict.popitem() that removes the most recently added item. It returns a two-value tuple in which first item is the key removed and second item is the value.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

print(data.popitem())
print(data)

('age', 25)
{'name': 'John'}

Note that since age was the last element of dictionary, it was removed.

Note

In Python versions below 3.7, a random item was removed by this method because dictionaries were not ordered.

Clearing Items

dict.clear() method takes the destructive approach and deletes all items from a dictionary.

CodeOutput

data = {
    'name': 'John',
    'age': 25,
}

print(data)

data.clear()
print(data)

{'name': 'John', 'age': 25}
{}