Dictionary Methods

Essential Dictionary Methods

Let’s look at some of the most frequently used dictionary methods:

1. clear()

The clear() method removes all items from a dictionary, leaving it empty.

my_dict = {"a": 1, "b": 2, "c": 3}
my_dict.clear()
print(my_dict)  # Output: {}

2. copy()

The copy() method creates a shallow copy of a dictionary. Changes made to the original dictionary won’t affect the copy, and vice versa (unless you modify mutable objects within the dictionary).

original_dict = {"x": 10, "y": [1, 2]}
copied_dict = original_dict.copy()
copied_dict["x"] = 20
print(original_dict)  # Output: {'x': 10, 'y': [1, 2]}
print(copied_dict)  # Output: {'x': 20, 'y': [1, 2]}

3. fromkeys()

The fromkeys() method creates a new dictionary from a given iterable (like a list or tuple) of keys, all assigned to a specified value.

keys = ["apple", "banana", "cherry"]
my_dict = dict.fromkeys(keys, 0) #assigns 0 to all keys
print(my_dict)  # Output: {'apple': 0, 'banana': 0, 'cherry': 0}

4. get()

The get() method retrieves the value associated with a specified key. Crucially, it avoids KeyError exceptions if the key doesn’t exist; instead, it returns a default value (None by default, or a specified value).

my_dict = {"name": "Alice", "age": 30}
print(my_dict.get("name"))  # Output: Alice
print(my_dict.get("city"))  # Output: None
print(my_dict.get("city", "Unknown")) # Output: Unknown

5. items()

The items() method returns a view object containing key-value pairs as tuples. This is useful for iterating through the dictionary.

my_dict = {"a": 1, "b": 2, "c": 3}
for key, value in my_dict.items():
    print(f"Key: {key}, Value: {value}")

6. keys()

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

my_dict = {"a": 1, "b": 2, "c": 3}
print(list(my_dict.keys()))  # Output: ['a', 'b', 'c']

7. pop()

The pop() method removes and returns the value associated with a specified key. It raises a KeyError if the key is not found.

my_dict = {"a": 1, "b": 2, "c": 3}
removed_value = my_dict.pop("b")
print(removed_value)  # Output: 2
print(my_dict)  # Output: {'a': 1, 'c': 3}

8. popitem()

The popitem() method removes and returns an arbitrary key-value pair (as a tuple). In Python 3.7+, it’s guaranteed to remove the last inserted item.

my_dict = {"a": 1, "b": 2, "c": 3}
removed_item = my_dict.popitem()
print(removed_item) # Output will vary depending on Python version prior to 3.7, but will be a (key,value) tuple
print(my_dict)

9. setdefault()

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

my_dict = {"a": 1, "b": 2}
value = my_dict.setdefault("c", 3) # adds key 'c' with value 3
print(value)  # Output: 3
print(my_dict)  # Output: {'a': 1, 'b': 2, 'c': 3}

value = my_dict.setdefault("a", 10) #'a' already exists, so its value is returned
print(value) #Output: 1

10. update()

The update() method merges another dictionary or iterable of key-value pairs into the current dictionary. Existing keys are updated, while new keys are added.

my_dict = {"a": 1, "b": 2}
my_dict.update({"c": 3, "b": 4}) # 'b' is updated, 'c' is added
print(my_dict)  # Output: {'a': 1, 'b': 4, 'c': 3}

11. values()

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

my_dict = {"a": 1, "b": 2, "c": 3}
print(list(my_dict.values()))  # Output: [1, 2, 3]