Dictionary Methods Guide

Here are a few useful methods that work on dictionary objects in Python. For a full list of dictionary methods, refer to the Python reference here: Python Reference Dictionary.

• Create an empty dictionary

    dict1 = {}
  

• Create a dictionary with key value pairs

    # Create a new dictionary with facts about the planet Mercury.
    mercury = {
        "name": "Mercury",
        "distance_from_sun_in_AU": 0.39,
        "rotational_period_in_earth_days": 58.6,
        "diameter_in_kilometers": 4879,
        "mass_in_kilograms": 3.3e23,
        "number_of_moons": 0
        }
  
    # Print individual values by using the key.
    print(mercury["name"])
    print(mercury["distance_from_sun_in_AU"])
  

• get(key):
  • Description: Returns the value for the specified key if the key is in the dictionary.
  • Parameters:
    • key: The key whose value you want to retrieve.
  • Example:

    person = {"name": "Alice", "age": 25}
    age = person.get("age")
    print(age)  # Outputs: 25
    

• keys():
  • Description: Returns a view object containing the keys of the dictionary.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    print(person.keys())  # Outputs: dict_keys(['name', 'age'])
    

• values():
  • Description: Returns a view object containing the values of the dictionary.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    print(person.values())  # Outputs: dict_values(['Alice', 25])
    

• items():
  • Description: Returns a view object containing key-value pairs (tuples) of the dictionary.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    print(person.items())  # Outputs: dict_items([('name', 'Alice'), ('age', 25)])
    

• pop(key):
  • Description: Removes the specified key and returns its value.
  • Parameters:
    • key: The key to remove.
  • Example:

    person = {"name": "Alice", "age": 25}
    age = person.pop("age")
    print(age)  # Outputs: 25
    print(person)  # Outputs: {'name': 'Alice'}
    

• popitem():
  • Description: Removes and returns the last inserted key-value pair as a tuple. Raises a KeyError if the dictionary is empty.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    item = person.popitem()
    print(item)  # Outputs: ('age', 25)
    print(person)  # Outputs: {'name': 'Alice'}
    

• update(other):
  • Description: Updates the dictionary with key-value pairs from another dictionary or an iterable of key-value pairs.
  • Parameters:
    • other: A dictionary or iterable of key-value pairs to update the dictionary.
  • Example:

    person = {"name": "Alice", "age": 25}
    new_info = {"age": 26, "city": "New York"}
    person.update(new_info)
    print(person)  # Outputs: {'name': 'Alice', 'age': 26, 'city': 'New York'}
    

• clear():
  • Description: Removes all elements from the dictionary, leaving it empty.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    person.clear()
    print(person)  # Outputs: {}
    

• copy():
  • Description: Returns a shallow copy of the dictionary.
  • Parameters: This method does not take any parameters.
  • Example:

    person = {"name": "Alice", "age": 25}
    person_copy = person.copy()
    print(person_copy)  # Outputs: {'name': 'Alice', 'age': 25}
    

• fromkeys(iterable, value):
  • Description: Creates a new dictionary with keys from an iterable and all values set to the specified value.
  • Parameters:
    • iterable: An iterable specifying the keys of the new dictionary.
    • value (optional): The value for all keys. Defaults to None.
  • Example:

    keys = ["name", "age", "city"]
    default_dict = dict.fromkeys(keys, "Unknown")
    print(default_dict)  # Outputs: {'name': 'Unknown', 'age': 'Unknown', 'city': 'Unknown'}