All Python Dictionary Methods with Examples, CBSE Class 12

Dictionaries are one of the most important data structures in the CBSE Class 12 Python syllabus. This guide covers every built-in dictionary method with clear examples and expected output, so you can answer any board exam question with confidence.

What is a Dictionary?

A dictionary stores data as key-value pairs inside curly braces {}. Keys must be unique and immutable (strings, numbers, or tuples). Values can be of any type.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}

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1. dict.get(key, default)

Returns the value for a key. If the key does not exist, it returns default instead of raising an error.

student = {"name": "Aman", "marks": 85}

print(student.get("name"))          # Key exists
print(student.get("age"))           # Key missing, no default
print(student.get("age", 18))       # Key missing, with default

Aman
None
18

Exam Tip: get() is safer than student["age"] because it does not throw a KeyError when the key is absent.

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2. dict.keys()

Returns a view object containing all the keys.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}
print(student.keys())
print(list(student.keys()))

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

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3. dict.values()

Returns a view object containing all the values.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}
print(student.values())
print(list(student.values()))

dict_values(['Aman', 85, 'Delhi'])
['Aman', 85, 'Delhi']

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4. dict.items()

Returns a view object of all key-value pairs as tuples.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}
print(student.items())

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

dict_items([('name', 'Aman'), ('marks', 85), ('city', 'Delhi')])
name -> Aman
marks -> 85
city -> Delhi

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5. dict.update(other_dict)

Adds key-value pairs from another dictionary. If a key already exists, its value is updated.

student = {"name": "Aman", "marks": 85}
student.update({"marks": 90, "city": "Delhi"})
print(student)

{'name': 'Aman', 'marks': 90, 'city': 'Delhi'}

Notice that marks was updated from 85 to 90, and city was added as a new key.

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6. dict.pop(key, default)

Removes the key and returns its value. If the key does not exist and no default is given, it raises a KeyError.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}

removed = student.pop("city")
print(removed)
print(student)

safe = student.pop("age", "Not found")
print(safe)

Delhi
{'name': 'Aman', 'marks': 85}
Not found

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7. dict.popitem()

Removes and returns the last inserted key-value pair as a tuple. Raises KeyError if the dictionary is empty.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}
last = student.popitem()
print(last)
print(student)

('city', 'Delhi')
{'name': 'Aman', 'marks': 85}

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8. dict.setdefault(key, default)

Returns the value of the key if it exists. If the key does not exist, it inserts the key with the given default value and returns that value.

student = {"name": "Aman", "marks": 85}

val1 = student.setdefault("name", "Unknown")
val2 = student.setdefault("city", "Delhi")

print(val1)
print(val2)
print(student)

Aman
Delhi
{'name': 'Aman', 'marks': 85, 'city': 'Delhi'}

Exam Tip: Unlike get(), setdefault() actually modifies the dictionary when the key is missing.

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9. dict.clear()

Removes all key-value pairs from the dictionary, making it empty.

student = {"name": "Aman", "marks": 85}
student.clear()
print(student)

{}

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10. dict.copy()

Returns a shallow copy of the dictionary. Changes to the copy do not affect the original.

original = {"name": "Aman", "marks": 85}
duplicate = original.copy()
duplicate["marks"] = 90

print(original)
print(duplicate)

{'name': 'Aman', 'marks': 85}
{'name': 'Aman', 'marks': 90}

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11. dict.fromkeys(keys, value)

Creates a new dictionary with the given keys, all set to the same value.

subjects = ["Maths", "Physics", "CS"]
marks = dict.fromkeys(subjects, 0)
print(marks)

{'Maths': 0, 'Physics': 0, 'CS': 0}

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12. del Statement

Not a method, but frequently tested. Deletes a specific key or the entire dictionary.

student = {"name": "Aman", "marks": 85, "city": "Delhi"}

del student["city"]       # Delete one key
print(student)

del student               # Delete entire dictionary
# print(student)          # NameError: name 'student' is not defined

{'name': 'Aman', 'marks': 85}

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13. in and not in Operators

Check whether a key exists in the dictionary.

student = {"name": "Aman", "marks": 85}

print("name" in student)
print("age" in student)
print("age" not in student)

True
False
True

Important: The in operator checks keys only, not values.

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Quick Reference Table

Method	What it Does	Returns
get(key, default)	Returns value for key	Value or default
keys()	All keys	dict_keys object
values()	All values	dict_values object
items()	All key-value pairs	dict_items of tuples
update(dict2)	Merges another dict	None
pop(key)	Removes key, returns value	Value
popitem()	Removes last pair	Tuple
setdefault(key, val)	Gets or inserts key	Value
clear()	Empties dictionary	None
copy()	Shallow copy	New dict
fromkeys(keys, val)	New dict from keys	New dict

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Common Exam Questions

Q1: What is the difference between get() and direct access using []?

Using student["age"] raises a KeyError if the key does not exist. Using student.get("age") returns None instead of raising an error. You can also pass a default value: student.get("age", 0).

Q2: What is the output of the following?

d = {"a": 1, "b": 2, "c": 3}
d.pop("b")
d.update({"d": 4})
print(d)
print(len(d))

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

Q3: Write the output:

d = {}
d.setdefault("x", []).append(1)
d.setdefault("x", []).append(2)
print(d)

{'x': [1, 2]}

The first call creates key "x" with an empty list, then appends 1. The second call finds the key already exists, returns the existing list, and appends 2.

Q4: Can a tuple be a dictionary key?

Yes, because tuples are immutable. Lists cannot be dictionary keys because they are mutable.

locations = {(28.6, 77.2): "Delhi", (19.0, 72.8): "Mumbai"}
print(locations[(28.6, 77.2)])

Delhi

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Tips for the Board Exam

1. get() vs [] is asked almost every year. Always mention that get() does not raise KeyError.
2. Remember that keys(), values(), and items() return view objects, not lists. Convert them with list() if needed.
3. update() both adds new keys and overwrites existing ones.
4. popitem() removes the last inserted item (Python 3.7+).
5. Dictionary keys must be immutable, strings, numbers, or tuples are allowed; lists are not.

Mastering these methods will help you handle dictionary-based questions in both the theory paper and practical exam.