Interesting facts about Dictionaries

 Dictionary Methods

Dictionaries come with several handy methods such as setdefault, update, pop, popitem, and clear.

my_dict = {'name': 'Alice', 'age': 25}

# setdefault

my_dict.setdefault('city', 'Unknown')

print(my_dict)  

# update

my_dict.update({'age': 26, 'city': 'New York'})

print(my_dict)  

# pop

age = my_dict.pop('age')

print(age)  # Output: 26

print(my_dict)  

# popitem

item = my_dict.popitem()

print(item) 

print(my_dict)  

# clear

my_dict.clear()

print(my_dict)  

#clcoding.com

{'name': 'Alice', 'age': 25, 'city': 'Unknown'}

{'name': 'Alice', 'age': 26, 'city': 'New York'}

26

{'name': 'Alice', 'city': 'New York'}

('city', 'New York')

{'name': 'Alice'}

{}

Ordered Dictionaries

As of Python 3.7, dictionaries maintain insertion order by default. The OrderedDict from the collections module was used for this purpose in earlier versions.

my_dict = {'first': 1, 'second': 2, 'third': 3}

print(my_dict)  

#clcoding.com

{'first': 1, 'second': 2, 'third': 3}

Merging Dictionaries

Starting with Python 3.9, you can use the | operator to merge dictionaries.

dict1 = {'a': 1, 'b': 2}

dict2 = {'b': 3, 'c': 4}

merged_dict = dict1 | dict2

print(merged_dict)  

#clcoding.com

{'a': 1, 'b': 3, 'c': 4}

Dictionary Views

The keys, values, and items methods return dictionary view objects, which are dynamic and reflect changes in the dictionary.

my_dict = {'name': 'Alice', 'age': 25}

keys_view = my_dict.keys()

print(keys_view)  

my_dict['city'] = 'New York'

print(keys_view) 

#clcoding.com

dict_keys(['name', 'age'])

dict_keys(['name', 'age', 'city'])

Default Values with get and defaultdict

Using the get method, you can provide a default value if the key is not found.

my_dict = {'name': 'Alice'}

print(my_dict.get('age', 'Not Found'))  

Not Found

With defaultdict from the collections module, you can provide default values for missing keys.

from collections import defaultdict

dd = defaultdict(int)

dd['a'] += 1

print(dd)  

#clcoding.com

defaultdict(<class 'int'>, {'a': 1})

Dictionary Comprehensions

Just like list comprehensions, you can create dictionaries using dictionary comprehensions.

squares = {x: x*x for x in range(6)}

print(squares)  

#clcoding.com

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Iterating Through Dictionaries

You can iterate through keys, values, or key-value pairs in a dictionary.

my_dict = {'name': 'Alice', 'age': 25}

for key in my_dict:

    print(key)  

for value in my_dict.values():

    print(value)  

for key, value in my_dict.items():

    print(key, value)  

#clcoding.com

name

age

Alice

25

name Alice

age 25

Keys Must Be Immutable and Unique

The keys in a dictionary must be immutable types (like strings, numbers, or tuples) and must be unique.

my_dict = {(1, 2): 'tuple key', 'name': 'Alice', 3.14: 'pi'}

print(my_dict)  

#clcoding.com

{(1, 2): 'tuple key', 'name': 'Alice', 3.14: 'pi'}

Efficient Lookup Time

Dictionaries have average O(1) time complexity for lookups, insertions, and deletions due to their underlying hash table implementation.

my_dict = {'a': 1, 'b': 2, 'c': 3}

print(my_dict['b'])  

#clcoding.com

2

Dynamic and Mutable

Dictionaries are mutable, which means you can change their content without changing their identity.

my_dict = {'name': 'Alice', 'age': 25}

my_dict['age'] = 26

my_dict['city'] = 'New York'

print(my_dict)  

#clcoding.com

{'name': 'Alice', 'age': 26, 'city': 'New York'}