Lesson 33 of 70 – Python Dictionary Methods

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Python Dictionary Methods

Python provides several built-in methods for working with dictionaries. These methods help you access, add, update, remove, and copy dictionary data.

Note: Dictionary methods are used to work efficiently with key-value pairs.

1. Common Dictionary Methods

Method	Purpose
get()	Returns the value of a specified key
keys()	Returns all dictionary keys
values()	Returns all dictionary values
items()	Returns key-value pairs
update()	Adds or updates dictionary items
pop()	Removes a specified key and returns its value
popitem()	Removes and returns the last inserted key-value pair
clear()	Removes all dictionary items
copy()	Creates a copy of the dictionary
setdefault()	Returns a value and optionally inserts a default value

2. get() Method

The get() method returns the value associated with a specified key.

student = {
    "name": "Amit",
    "age": 20
}

print(student.get("name"))

Output:
Amit

3. get() for a Missing Key

If the key does not exist, get() returns None by default.

student = {
    "name": "Amit"
}

print(student.get("age"))

Output:
None

4. get() with a Default Value

You can provide a default value that will be returned when the key does not exist.

student = {
    "name": "Amit"
}

print(student.get("age", 18))

Output:
18

5. keys() Method

The keys() method returns a view containing all dictionary keys.

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

print(student.keys())

Output:
dict_keys(['name', 'age', 'course'])

6. Looping Through keys()

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

for key in student.keys():
    print(key)

Output:
name
age
course

7. values() Method

The values() method returns a view containing all dictionary values.

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

print(student.values())

Output:
dict_values(['Amit', 20, 'Python'])

8. Looping Through values()

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

for value in student.values():
    print(value)

Output:
Amit
20
Python

9. items() Method

The items() method returns a view containing all key-value pairs.

student = {
    "name": "Amit",
    "age": 20
}

print(student.items())

Output:
dict_items([('name', 'Amit'), ('age', 20)])

10. Looping Through items()

student = {
    "name": "Amit",
    "age": 20
}

for key, value in student.items():
    print(key, ":", value)

Output:
name : Amit
age : 20

11. update() Method

The update() method adds new key-value pairs or updates existing keys.

student = {
    "name": "Amit",
    "age": 20
}

student.update({"course": "Python"})

print(student)

Output:
{'name': 'Amit', 'age': 20, 'course': 'Python'}

12. update() Existing Value

If the key already exists, update() changes its value.

student = {
    "name": "Amit",
    "age": 20
}

student.update({"age": 21})

print(student)

Output:
{'name': 'Amit', 'age': 21}

13. pop() Method

The pop() method removes the specified key and returns its associated value.

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

age = student.pop("age")

print(age)
print(student)

Output:
20
{'name': 'Amit', 'course': 'Python'}

14. pop() with Default Value

You can provide a default value to pop(). This avoids a KeyError when the specified key is missing.

student = {
    "name": "Amit"
}

result = student.pop("age", "Not Found")

print(result)

Output:
Not Found

15. popitem() Method

The popitem() method removes and returns the last inserted key-value pair.

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

item = student.popitem()

print(item)
print(student)

Output:
('course', 'Python')
{'name': 'Amit', 'age': 20}

16. popitem() on an Empty Dictionary

Calling popitem() on an empty dictionary raises a KeyError.

student = {}

student.popitem()

Result:
KeyError: 'popitem(): dictionary is empty'

17. clear() Method

The clear() method removes all key-value pairs from a dictionary.

student = {
    "name": "Amit",
    "age": 20,
    "course": "Python"
}

student.clear()

print(student)

Output:
{}

18. copy() Method

The copy() method creates a shallow copy of a dictionary.

student = {
    "name": "Amit",
    "age": 20
}

new_student = student.copy()

print(new_student)

Output:
{'name': 'Amit', 'age': 20}

19. Changing a Dictionary Copy

Changing a separate dictionary created with copy() does not change the top-level contents of the original dictionary.

student = {
    "name": "Amit",
    "age": 20
}

new_student = student.copy()

new_student["age"] = 21

print("Original:", student)
print("Copy:", new_student)

Output:
Original: {'name': 'Amit', 'age': 20}
Copy: {'name': 'Amit', 'age': 21}

20. setdefault() Method

The setdefault() method returns the value of a key. If the key does not exist, it inserts the key with a specified default value.

student = {
    "name": "Amit"
}

age = student.setdefault("age", 20)

print(age)
print(student)

Output:
20
{'name': 'Amit', 'age': 20}

21. setdefault() with Existing Key

If the key already exists, setdefault() returns its existing value and does not replace it with the default value.

student = {
    "name": "Amit",
    "age": 20
}

result = student.setdefault("age", 25)

print(result)
print(student)

Output:
20
{'name': 'Amit', 'age': 20}

22. fromkeys() Method

The fromkeys() method creates a new dictionary using the specified keys and an optional common value.

keys = ("name", "age", "course")

student = dict.fromkeys(keys)

print(student)

Output:
{'name': None, 'age': None, 'course': None}

23. fromkeys() with a Common Value

keys = ("name", "age", "course")

student = dict.fromkeys(keys, "Not Available")

print(student)

Output:
{'name': 'Not Available', 'age': 'Not Available', 'course': 'Not Available'}

24. del vs pop()

Feature	del	pop()
Removes item	Yes	Yes
Returns removed value	No	Yes
Can provide default value	No	Yes

25. Practical Example

student = {
    "name": "Rahul",
    "course": "Python",
    "fees": 5000
}

print("Name:", student.get("name"))

student.update({"fees": 6000})

print("Updated Fees:", student["fees"])

for key, value in student.items():
    print(key, ":", value)

Output:
Name: Rahul
Updated Fees: 6000
name : Rahul
course : Python
fees : 6000

26. Key Points

get() retrieves a value safely.
keys() returns dictionary keys.
values() returns dictionary values.
items() returns key-value pairs.
update() adds or changes items.
pop() removes a specified key and returns its value.
popitem() removes and returns the last inserted key-value pair.
clear() removes all dictionary items.
copy() creates a shallow copy.
setdefault() retrieves a value or creates a key with a default value.
fromkeys() creates a dictionary from a sequence of keys.

🧠 Quick Quiz

Question: Which dictionary method returns all key-value pairs?

keys()
values()
items()
pairs()

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