setdefault() retrieves the value of a specified key in a dictionary

Getting the value of the input key

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('b')
print(x)
print(my_dict)

Two
{'a': 'One', 'b': 'Two', 'c': 'Three'}

If input key is not available then key is added.

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('d')
print(x)
print(my_dict)

None
{'a': 'One', 'b': 'Two', 'c': 'Three', 'd': None}

Adding new key with value

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('d','Four')
print(x)
print(my_dict)

Four
{'a': 'One', 'b': 'Two', 'c': 'Three', 'd': 'Four'}

Example 1: Setting Default Value with a Different Data Type

my_dict = {'a': 1, 'b': 2}
x = my_dict.setdefault('c', [3, 4])
print(x)  # Output: [3, 4]
print(my_dict)  # Output: {'a': 1, 'b': 2, 'c': [3, 4]}

Example 2: Using setdefault() with Nested Dictionaries

nested_dict = {'person': {'name': 'Alice'}}
nested_dict.setdefault('person', {}).setdefault('age', 25)
print(nested_dict)  # Output: {'person': {'name': 'Alice', 'age': 25}}

Example 3: Counting Occurrences in a List with setdefault()

my_list = ['apple', 'banana', 'apple', 'orange']
count_dict = {}
for item in my_list:
    count_dict.setdefault(item, 0)
    count_dict[item] += 1
print(count_dict)  # Output: {'apple': 2, 'banana': 1, 'orange': 1}

Example 4: Handling Missing Keys with Default Values

data = {'name': 'Alice'}
age = data.setdefault('age', 30)
print(age)  # Output: 30
print(data)  # Output: {'name': 'Alice', 'age': 30}

Example 5: Appending to a List in a Dictionary Using setdefault()

my_dict = {}
my_dict.setdefault('fruits', []).append('apple')
my_dict.setdefault('fruits', []).append('banana')
print(my_dict)  # Output: {'fruits': ['apple', 'banana']}

Example 6: Grouping Strings by Length Using setdefault()

words = ['cat', 'dog', 'elephant', 'bird']
length_dict = {}
for word in words:
    length_dict.setdefault(len(word), []).append(word)
print(length_dict)  # Output: {3: ['cat', 'dog'], 8: ['elephant'], 4: ['bird']}

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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