Dictionaries

Dictionaries#

A dictionary is a collection of unordered, modifiable (mutable) paired (key: value) data type.

Creating a Dictionary#

To create a dictionary we use curly brackets, {} or the dict() built-in function.

empty_dict = {}
empty_dict

{}

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d

{'key1': 'value1', 'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
person

{'first_name': 'Aurora',
 'last_name': 'Luna',
 'age': 6,
 'country': 'Indonesia',
 'skills': ['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
 'address': {'street': 'Jl. Jalan', 'zipcode': '123456'}}

The dictionary above shows that a value could be any data types: string, boolean, list, tuple, set or a dictionary.

Dictionary Length#

It checks the number of ‘key: value’ pairs in the dictionary.

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
len(d)

4

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
len(person)

6

Accessing Dictionary Items#

We can access Dictionary items by referring to its key name.

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
print(d["key1"])
print(d["key4"])

value1
value4

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
print(person["first_name"])
print(person["country"])
print(person["skills"])
print(person["skills"][0])
print(person["address"]["street"])  # Space street
# print(person['city']) # Running this will raise KeyError: 'city'

Aurora
Indonesia
['JavaScript', 'React', 'Node', 'MongoDB', 'Python']
JavaScript
Jl. Jalan

Accessing an item by key name raises an error if the key does not exist. To avoid this error first we have to check if a key exist or we can use the get() method. The get() method returns None, which is a NoneType object data type, if the key does not exist.

print(person.get("first_name"))
print(person.get("country"))
print(person.get("skills"))
print(person.get("city"))

Aurora
Indonesia
['JavaScript', 'React', 'Node', 'MongoDB', 'Python']
None

Adding Items to a Dictionary#

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d["key5"] = "value5"
d

{'key1': 'value1',
 'key2': 'value2',
 'key3': 'value3',
 'key4': 'value4',
 'key5': 'value5'}

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
person["job_title"] = "Student"
person["skills"].append("TensorFlow")
person

{'first_name': 'Aurora',
 'last_name': 'Luna',
 'age': 6,
 'country': 'Indonesia',
 'skills': ['JavaScript', 'React', 'Node', 'MongoDB', 'Python', 'TensorFlow'],
 'address': {'street': 'Jl. Jalan', 'zipcode': '123456'},
 'job_title': 'Student'}

Modifying Items in a Dictionary#

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d["key1"] = "value-one"
d

{'key1': 'value-one', 'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
person["last_name"] = "Wulan"
person["country"] = "New Zealand"
person

{'first_name': 'Aurora',
 'last_name': 'Wulan',
 'age': 6,
 'country': 'New Zealand',
 'skills': ['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
 'address': {'street': 'Jl. Jalan', 'zipcode': '123456'}}

Checking Keys in a Dictionary#

We use the in operator to check if a key exist in a dictionary.

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
print("key2" in d)
print("key5" in d)

True
False

Removing Key and Value Pairs from a Dictionary#

  • pop(key): removes the item with the specified key name

  • popitem(): removes the last item

  • del: removes an item with specified key name

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d.pop("key1")
d

{'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d.popitem()

('key4', 'value4')

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
del d["key2"]
d

{'key1': 'value1', 'key3': 'value3', 'key4': 'value4'}

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
person.pop("address")
person.popitem()
del person["country"]
person

{'first_name': 'Aurora', 'last_name': 'Luna', 'age': 6}

Changing Dictionary to a List of Items#

The items() method changes dictionary to a list of tuples.

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d.items()

dict_items([('key1', 'value1'), ('key2', 'value2'), ('key3', 'value3'), ('key4', 'value4')])

person = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "age": 6,
    "country": "Indonesia",
    "skills": ["JavaScript", "React", "Node", "MongoDB", "Python"],
    "address": {"street": "Jl. Jalan", "zipcode": "123456"},
}
person.items()

dict_items([('first_name', 'Aurora'), ('last_name', 'Luna'), ('age', 6), ('country', 'Indonesia'), ('skills', ['JavaScript', 'React', 'Node', 'MongoDB', 'Python']), ('address', {'street': 'Jl. Jalan', 'zipcode': '123456'})])

Clearing a Dictionary#

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
print(d.clear())

None

Deleting a Dictionary#

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
del d

Copy a Dictionary#

We can copy a dictionary using a copy() method. Using copy we can avoid mutation of the original dictionary.

d1 = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
d2 = d1.copy()
d2

{'key1': 'value1', 'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

Getting Dictionary Keys as a List#

The keys() method gives us all the keys of a a dictionary as a list.

d = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
keys = d.keys()
keys

dict_keys(['key1', 'key2', 'key3', 'key4'])

Getting Dictionary Values as a List#

The values() method gives us all the values of a a dictionary as a list.

dct = {"key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"}
values = dct.values()
values

dict_values(['value1', 'value2', 'value3', 'value4'])
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