Dictionaries in Python

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A Python dictionary is a data structure that stores the value in key: value pairs. Values in a dictionary can be of any data type and can be duplicated, whereas keys can’t be repeated and must be immutable.

Example: Here, The data is stored in key:value pairs in dictionaries, which makes it easier to find values.

d = {1: 'Geeks', 2: 'For', 3: 'Geeks'}
print(d)

{1: 'Geeks', 2: 'For', 3: 'Geeks'}

How to Create a Dictionary

In Python, a dictionary can be created by placing a sequence of elements within curly {} braces, separated by a ‘comma’.

# create dictionary using { }
d1 = {1: 'Geeks', 2: 'For', 3: 'Geeks'}
print(d1)

# create dictionary using dict() constructor
d2 = dict(a = "Geeks", b = "for", c = "Geeks")
print(d2)

{1: 'Geeks', 2: 'For', 3: 'Geeks'}
{'a': 'Geeks', 'b': 'for', 'c': 'Geeks'}

• From Python 3.7 Version onward, Python dictionary are Ordered.
• Dictionary keys are case sensitive: the same name but different cases of Key will be treated distinctly.
• Keys must be immutable: This means keys can be strings, numbers, or tuples but not lists.
• Keys must be unique: Duplicate keys are not allowed and any duplicate key will overwrite the previous value.
• Dictionary internally uses Hashing. Hence, operations like search, insert, delete can be performed in Constant Time.

Accessing Dictionary Items

We can access a value from a dictionary by using the key within square brackets orget()method.

d = { "name": "Alice", 1: "Python", (1, 2): [1,2,4] }

# Access using key
print(d["name"])

# Access using get()
print(d.get("name"))  

Alice
Alice

Adding and Updating Dictionary Items

We can add new key-value pairs or update existing keys by using assignment.

d = {1: 'Geeks', 2: 'For', 3: 'Geeks'}

# Adding a new key-value pair
d["age"] = 22

# Updating an existing value
d[1] = "Python dict"

print(d)

{1: 'Python dict', 2: 'For', 3: 'Geeks', 'age': 22}

Removing Dictionary Items

We can remove items from dictionary using the following methods:

• del: Removes an item by key.
• pop(): Removes an item by key and returns its value.
• clear(): Empties the dictionary.
• popitem(): Removes and returns the last key-value pair.

d = {1: 'Geeks', 2: 'For', 3: 'Geeks', 'age':22}

# Using del to remove an item
del d["age"]
print(d)

# Using pop() to remove an item and return the value
val = d.pop(1)
print(val)

# Using popitem to removes and returns
# the last key-value pair.
key, val = d.popitem()
print(f"Key: {key}, Value: {val}")

# Clear all items from the dictionary
d.clear()
print(d)

{1: 'Geeks', 2: 'For', 3: 'Geeks'}
Geeks
Key: 3, Value: Geeks
{}

Iterating Through a Dictionary

We can iterate over keys [using keys() method] , values [using values() method] or both [using item() method] with a for loop.

d = {1: 'Geeks', 2: 'For', 'age':22}

# Iterate over keys
for key in d:
    print(key)

# Iterate over values
for value in d.values():
    print(value)

# Iterate over key-value pairs
for key, value in d.items():
    print(f"{key}: {value}")

1
2
age
Geeks
For
22
1: Geeks
2: For
age: 22

Read in detail – Ways to Iterating Over a Dictionary

Nested Dictionaries

Example of Nested Dictionary:

d = {1: 'Geeks', 2: 'For',
        3: {'A': 'Welcome', 'B': 'To', 'C': 'Geeks'}}

print(d)

{1: 'Geeks', 2: 'For', 3: {'A': 'Welcome', 'B': 'To', 'C': 'Geeks'}}

Read in Detail: Python Nested Dictionary

Python Dictionary Operation Programs

• Dictionary Creation Programs.
• Dictionary Add/Append Programs.
• Dictionary Removal Programs.
• Dictionary Access Programs.
• Dictionary Conversion Programs.
• Dictionary Programs involving Lists.
• Dictionary Programs involving String, Tuple and Set.

Python Dictionary Problems

• Length of a Dictionary
• Check if a Key Exists
• Access a Value by Key
• Remove a Key from a Dictionary
• Remove keys with substring values
• Sum All Numeric Values in a Dictionary
• Find Keys with Maximum Value
• Remove Duplicates from a Dictionary
• Filter Dictionary by Key Prefix
• Count Frequency of Elements Using Dictionary
• Check if two arrays are equal or not
• Max distance between two occurrences in array
• 2 Sum – Count Pairs with target sum
• 3 Sum – Count all triplets with target sum
• Count all pairs with absolute difference equal to k
• Remove minimum elements such that no common elements exist in two arrays
• Check If Array Pair Sums Divisible by k
• Longest subarray with sum divisible by K
• Longest Subarray having Majority Elements Greater Than K
• Count distinct elements in every window of size k

Related Dictionary Articles

• Dictionary Comprehension
• Dictionary Methods
• Python Dictionary Exercise
• Python Dictionary Quiz

Python Dictionary – FAQs

How to use dictionaries in Python?

Dictionaries in Python are used to store key-value pairs. They are unordered, mutable, and can contain any Python objects as values.

# Creating a dictionary
my_dict = {‘key1’: ‘value1’, ‘key2’: ‘value2’}
# Accessing values by keys
print(my_dict[‘key1’]) # Output: value1

# Modifying values
my_dict[‘key2’] = ‘new_value’
# Adding new key-value pairs
my_dict[‘key3’] = ‘value3’
# Removing a key-value pair
del my_dict[‘key1’]

How to print dictionaries in Python?

You can use print() to display the contents of a dictionary. You can print the entire dictionary or specific elements by accessing keys or values.

my_dict = {‘name’: ‘Alice’, ‘age’: 30}
# Printing the entire dictionary
print(my_dict)
# Printing specific elements
print(my_dict[‘name’]) # Output: Alice

How to declare a dictionary in Python?

You can declare a dictionary by enclosing key-value pairs within curly braces {}.

# Empty dictionary
empty_dict = {}
# Dictionary with initial values
my_dict = {‘key1’: ‘value1’, ‘key2’: ‘value2’}

What are dictionary keys and values in Python?

In a dictionary, keys are unique identifiers that are used to access values. Values are the data associated with those keys.

my_dict = {‘name’: ‘Alice’, ‘age’: 30}
# Accessing keys and values
print(my_dict.keys()) # Output: dict_keys([‘name’, ‘age’])
print(my_dict.values()) # Output: dict_values([‘Alice’, 30])

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