Python Program To Create A Dictionary With A Dictionary Literal

Dictionaries are used to store data values in key:value pairs. Unlike other data types that hold only a single value as an element, dictionaries use key-value pairs to make data access more effective.

Dictionary keys must be unique, so no duplicate keys are allowed. Dictionary items are ordered (as of Python 3.7+), changeable, and mutable. This means we can add or remove items after the dictionary is created.

Creating a Dictionary with Dictionary Literals

We can create a dictionary using curly brackets {}. Place elements inside curly brackets, separate keys and values with colons :, and separate each key-value pair with commas.

Basic Dictionary Creation

Here's how to create different types of dictionaries using dictionary literals ?

# Dictionary with integers and strings
flowers = {1: 'rose', 2: 'lily', 3: 'jasmine'}

# Dictionary with integers only
numbers = {1: 5, 3: 7, 8: 6, 9: 4}

# Dictionary with strings and lists (mixed types)
heroes = {'spider': 'man', 'captain': 'america', 'iron': ['tony', 'starks']}

# Empty dictionary
empty_dict = {}

print("Flowers:", flowers)
print("Numbers:", numbers)
print("Heroes:", heroes)
print("Empty:", empty_dict)
print("Length of flowers dict:", len(flowers))

Flowers: {1: 'rose', 2: 'lily', 3: 'jasmine'}
Numbers: {1: 5, 3: 7, 8: 6, 9: 4}
Heroes: {'spider': 'man', 'captain': 'america', 'iron': ['tony', 'starks']}
Empty: {}
Length of flowers dict: 3

Using the dict() Constructor

Python also provides the built-in dict() constructor to create dictionaries ?

# Creating dictionary using dict() constructor
colors = dict(red='#FF0000', green='#00FF00', blue='#0000FF')
print("Colors:", colors)

# Converting list of tuples to dictionary
pairs = [('name', 'Alice'), ('age', 25), ('city', 'New York')]
person = dict(pairs)
print("Person:", person)

Colors: {'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'}
Person: {'name': 'Alice', 'age': 25, 'city': 'New York'}

Special Dictionary Types

Python's collections module provides specialized dictionary types for specific use cases.

OrderedDict

Maintains insertion order (though regular dictionaries now preserve order in Python 3.7+) ?

from collections import OrderedDict

fruits = OrderedDict()
fruits[1] = "apple"
fruits[2] = "mango"
fruits[3] = "cherry"

for key, value in fruits.items():
    print(f"{key}: {value}")

1: apple
2: mango
3: cherry

defaultdict

Provides default values for non-existing keys ?

from collections import defaultdict

def default_value():
    return "not existing"

grades = defaultdict(default_value)
grades['Alice'] = 'A'
grades['Bob'] = 'B'

print("Alice's grade:", grades['Alice'])
print("Charlie's grade:", grades['Charlie'])  # Non-existing key

Alice's grade: A
Charlie's grade: not existing

Counter

Counts occurrences of elements ?

from collections import Counter

text = 'an apple a day keeps doctor away'
word_count = Counter(text.split())

print("Word frequencies:")
print(word_count)
print("Most common word:", word_count.most_common(1))

Word frequencies:
Counter({'an': 1, 'apple': 1, 'a': 1, 'day': 1, 'keeps': 1, 'doctor': 1, 'away': 1})
Most common word: [('an', 1)]

Key Features Summary

Conclusion

Dictionary literals using curly brackets {} provide the most straightforward way to create dictionaries in Python. Use specialized dictionary types from the collections module when you need specific functionality like default values or element counting.