Python Dictionaries (Python for Beginners)

Python dictionaries are an unordered collection of key-value pairs. Dictionaries are a mappings data type used to store collections of data.

The 4 data types that store collections are: dictionaries, lists, sets and tuples, which we’ll cover in other lessons.

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Example Python Dictionary

Python dictionaries are created using curl brackets ({})

# Example Dictionary
d = {
        'name': 'JC', 
        'last_name': 'Chouinard'
    }
d

In the output, we know that the element is a dictionary based on the curly brackets.

{'name': 'JC', 'last_name': 'Chouinard'}

Dictionaries don’t allow duplicates

# No duplicates
{
    'name': 'JC', 
    'name': 'JC'
}

The output does not show duplicate values.

{'name': 'JC'}

Dictionaries Have Keys and Values

## Key,value pairs
d = {
    'a':1,
    'b':2,
    'c':3
}

# Access the value using the key
d['a']

Values Can Have Multiple Data Types

# Storing data types in dicts
d = {
    'str':'hello',
    'bool':False,
    'list':[1,2,3],
    'int':10
}
print(type(d))
print(type(d['bool']))

<class 'dict'>
<class 'bool'>

Creating a Dictionary

Create an empty dictionary

# Initialize empty dictionary
d = dict()
print(d)
d = {}
print(d)

{}
{}

Create a Dictionary Using a Constructor

# Constructor
dict(name='JC',last_name='Chouinard')

{'name': 'JC', 'last_name': 'Chouinard'}

Create a Dictionary From Keys

# Create dict from keys
keys = ['a','b','c']
value = 0
dict.fromkeys(keys,value)

{'a': 0, 'b': 0, 'c': 0}

Searching a Dictionary

Let’s talk about how to search through a dictionary.

Take this dictionary to start with:

# create dict 
my_dict = dict(
    name='David',
    last_name='Attenborough',
    birth='1926-05-09',
    occupations=['Broadcaster','naturalist'],
    family={
        'spouse':'Jane Ebsworth Oriel',
        'children':2
        }
    )
my_dict

{'name': 'David',
 'last_name': 'Attenborough',
 'birth': '1926-05-09',
 'occupations': ['Broadcaster', 'naturalist'],
 'family': {'spouse': 'Jane Ebsworth Oriel', 'children': 2}}

Show Dictionary Keys

# Keys
my_dict.keys()

dict_keys(['name', 'last_name', 'birth', 'occupations', 'family'])

Show Dictionary Values

# Values
my_dict.values()

dict_values(['David', 'Attenborough', '1926-05-09', ['Broadcaster', 'naturalist'], {'spouse': 'Jane Ebsworth Oriel', 'children': 2}])

Search Dictionary Value using Get

# Get
my_dict.get('name')

'David'

Search Dictionary Nested-Value using Get

# Keys
my_dict.keys()

dict_keys(['name', 'last_name', 'birth', 'occupations', 'family'])

# Nested Dict
my_dict['family'].get('spouse')

'Jane Ebsworth Oriel'

# Nested Dict
my_dict['family']['spouse']

'Jane Ebsworth Oriel'

Modify Values of Python Dictionaries

Modify a Single Value

# Modify value
my_dict['birth'] = '1926-05-08'
my_dict['birth']

'1926-05-08'

Add Items

# Assign value to key
my_dict['known_for'] = 'Wildife Documentaries'
my_dict['known_for']

'Wildife Documentaries'

Perform Multiple Changes at Once

# Perform multiple changes at once
my_dict.update({
    'known_for':'Planet Earth',
    'works_for':'BBC'
})

my_dict

{'name': 'David',
 'last_name': 'Attenborough',
 'birth': '1926-05-08',
 'occupations': ['Broadcaster', 'naturalist'],
 'family': {'spouse': 'Jane Ebsworth Oriel', 'children': 2},
 'known_for': 'Planet Earth',
 'works_for': 'BBC'}

Remove Items from a Dictionary

Remove Specific Item from a Python Dictionary

# Remove specific Item
my_dict.pop('birth')
my_dict

{'name': 'David',
 'last_name': 'Attenborough',
 'occupations': ['Broadcaster', 'naturalist'],
 'family': {'spouse': 'Jane Ebsworth Oriel', 'children': 2},
 'known_for': 'Planet Earth',
 'works_for': 'BBC'}

Remove Last Item from a Dictionary

# Remove last item
my_dict.popitem()
my_dict

{'name': 'David',
 'last_name': 'Attenborough',
 'occupations': ['Broadcaster', 'naturalist'],
 'family': {'spouse': 'Jane Ebsworth Oriel', 'children': 2},
 'known_for': 'Planet Earth'}

Looping Through a Python Dictionary

# Create dict
my_dict = dict(
    name='JC',
    last_name='Chouinard',
    domain='jcchouinard.com',
    twitter='ChouinardJC'
)

Loop and Print Dictionary Keys

Two ways to loop through a dictionary and print its keys.

# Print Keys
for x in my_dict:
    print(x)

name
last_name
domain
twitter

# Print Keys
for x in my_dict.keys():
    print(x)

name
last_name
domain
twitter

Loop and Print Dictionary Values

Two ways to loop through a dictionary and print its values.

# Print values
for x in my_dict:
    print(my_dict[x])

JC
Chouinard
jcchouinard.com
ChouinardJC

# print values
for x in my_dict.values():
    print(x)

JC
Chouinard
jcchouinard.com
ChouinardJC

Loop and Print Dictionary Keys and Values

Use the items() method on the dictionary to loop through each key, value pair.

# Print Keys and values
for x in my_dict.items():
    print(x[0], x[1])

name JC
last_name Chouinard
domain jcchouinard.com
twitter ChouinardJC

Other Python Dictionary Methods

# Create dict
my_dict = dict(
    name='JC',
    last_name='Chouinard',
    domain='jcchouinard.com',
    twitter='ChouinardJC'
)

Add if not Existing: setdefault()

# Add if not existing
my_dict.setdefault('employer','Tripadvisor')
my_dict

{'name': 'JC',
 'last_name': 'Chouinard',
 'domain': 'jcchouinard.com',
 'twitter': 'ChouinardJC',
 'employer': 'Tripadvisor'}

# But don't change if key exist
my_dict.setdefault('name','Jean-Christophe')
my_dict

{'name': 'JC',
 'last_name': 'Chouinard',
 'domain': 'jcchouinard.com',
 'twitter': 'ChouinardJC',
 'employer': 'Tripadvisor'}

Clear Dictionary: clear()

# Empty dict
my_dict.clear()
my_dict

{}

Conclusion

This was a very simple introduction to Python Dictionaries.

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Jean-Christophe Chouinard

SEO Strategist at Tripadvisor, ex- Seek (Melbourne, Australia). Specialized in technical SEO. Writer in Python, Information Retrieval, SEO and machine learning. Guest author at SearchEngineJournal, SearchEngineLand and OnCrawl.

Python Dictionaries