Here is a clear, complete, and exam-oriented explanation of the Functions & Methods of Dictionary in Python, perfect for BCA/MCA/B.Tech students.
Functions & Methods of Dictionary in Python
Python provides powerful built-in functions and methods to work with dictionaries efficiently.
These help in accessing, modifying, updating, and removing key–value pairs.
We divide them into:
- Built-in Functions used with dictionaries
- Dictionary Methods
1. Built-in Functions for Dictionaries
These functions work on various Python data types, including dictionaries.
1. len()
Returns the number of key–value pairs.
d = {"a": 1, "b": 2}
print(len(d)) # 2
2. type()
Returns the type of object.
print(type(d)) # <class 'dict'>
3. str()
Converts dictionary into a readable string format.
print(str(d))
4. dict()
Creates a new dictionary.
d = dict(name="John", age=20)
2. Dictionary Methods (Very Important for Exams)
These methods are used only for dictionary objects.
1. get(key, default)
Returns value of a key.
If key does not exist → returns None or a default value.
d = {"a": 1, "b": 2}
print(d.get("a")) # 1
print(d.get("x", "Not found")) # Not found
2. keys()
Returns all keys as a view object.
print(d.keys()) # dict_keys(['a', 'b'])
3. values()
Returns all values.
print(d.values()) # dict_values([1, 2])
4. items()
Returns key–value pairs as tuples.
print(d.items()) # dict_items([('a', 1), ('b', 2)])
5. update(other_dict)
Adds or overwrites key–value pairs from another dictionary.
d1 = {"a": 1, "b": 2}
d2 = {"b": 3, "c": 4}
d1.update(d2)
print(d1) # {'a': 1, 'b': 3, 'c': 4}
6. pop(key, default)
Removes the item with the specified key.
d = {"a": 1, "b": 2}
print(d.pop("a")) # 1
If key not found → returns default value (if provided).
7. popitem()
Removes and returns the last key–value pair (Python 3.7+).
d = {"a": 1, "b": 2}
print(d.popitem()) # ('b', 2)
8. clear()
Removes all items from the dictionary.
d.clear()
print(d) # {}
9. copy()
Returns a shallow copy of the dictionary.
d1 = {"a": 1, "b": 2}
d2 = d1.copy()
10. setdefault(key, default)
- If key exists → returns its value
- If key does not exist → inserts the key with default value
d = {"name": "Ram"}
print(d.setdefault("age", 20)) # Adds age: 20
print(d) # {'name': 'Ram', 'age': 20}
11. fromkeys(iterable, value)
Creates a new dictionary with keys from iterable and same value.
keys = ["a", "b", "c"]
new_dict = dict.fromkeys(keys, 0)
print(new_dict) # {'a': 0, 'b': 0, 'c': 0}
12. __contains__(key) (using in)
Checks if key exists.
print("a" in d) # True
13. __delitem__(key) (using del)
Deletes an item.
del d["a"]
Full Example of Major Methods
student = {"name": "John", "age": 21, "grade": "A"}
print(student.keys())
print(student.values())
print(student.items())
student.update({"age": 22, "city": "Delhi"})
print(student)
student.pop("grade")
print(student)
student.setdefault("course", "BCA")
print(student)
Summary Table of Dictionary Methods
| Method | Description |
|---|---|
| get() | Returns value of key |
| keys() | Returns list of keys |
| values() | Returns list of values |
| items() | Returns list of key–value pairs |
| update() | Adds/updates dictionary |
| pop() | Removes key and returns value |
| popitem() | Removes last key–value pair |
| clear() | Removes all items |
| copy() | Copies dictionary |
| setdefault() | Adds key if not exists |
| fromkeys() | Creates new dictionary from keys |