Python Dictionaries: Your Secret Weapon for Data Agility

Python dictionaries are a fundamental and versatile data structure. They allow you to store data in key value pairs, providing an efficient way to organize and manage information.

A dictionary is like a real world dictionary where you look up a word (“Key”) to find its definition (“Value”). In Python:

• Key: A unique identifier for a piece of data. Keys must be immutable (e.g., strings, numbers, tuples).

• Value: The data associated with a key. Values can be of any data type (e.g., strings, numbers, lists, even other dictionaries).

Key Characteristics of a Dictionary:

• Mutable: You can add, modify, or remove key-value pairs after a dictionary is created.

• Unique Keys: A dictionary cannot contain duplicate keys. If you try to assign a value to an existing key, the old value will be overwritten.

• Values: In dictionary multiple different keys can have the same value.

• Ordered: Starting with Python 3.7, dictionary preserve the means that items are stored in the order they were added. In python 3.6 and earlier, dictionaries are unordered

Creating Dictionaries:

You can create dictionaries using curly braces {} :

student = {
    "name": "Alice",
    "age": 20,
    "major": "Computer Science"
}
print(student)

Accessing Values:

You access values using their corresponding keys within square brackets [] :

student = {"name": "Alice", "age": 20}
print(student["name"])  # Output: Alice
print(student["age"])    # Output: 20

#Accessing a value using get()
print(student.get("name")) #Output: Alice
print(student.get("major")) #Output: None
print(student.get("major", "Unknown")) #Output: Unknown

Modifying Dictionaries:

• Adding/Updating: To add a new key-value pair or update an existing one:

    student = {"name": "Alice", "age": 20}
    student["major"] = "Computer Science"  # Add a new key-value pair
    student["age"] = 21  # Update the value for "age"
    print(student)
  

• Removing:

  • pop(key): Removes the key and returns its value. Raises a KeyError if the key is not found.

      student = {"name": "Alice", "age": 20, "major": "Computer Science"}
      age = student.pop("age")
      print(age) # Output: 20
      print(student) #Output:{'name': 'Alice', 'major': 'Computer Science'}
    

  • popitem(): Removes and returns an arbitrary (key, value) pair. (Removes the last inserted item in Python 3.7+).

      student = {"name": "Alice", "age": 20, "major": "Computer Science"}
      item = student.popitem()
      print(item)    # Output: ('major', 'Computer Science') (or another pair)
      print(student)
    

  • del: Deletes a key-value pair. Raises a KeyError if the key is not found.

      student = {"name": "Alice", "age": 20, "major": "Computer Science"}
      del student["age"]
      print(student)   # Output: {'name': 'Alice', 'major': 'Computer Science'}
    

  • clear(): Removes all items from the dictionary, leaving it empty.

      student = {"name": "Alice", "age": 20, "major": "Computer Science"}
      student.clear()
      print(student)  # Output: {}
    

  • Iterating Through Dictionaries:

    You can iterate over dictionaries in various ways:

    • Iterating over keys (default):

        student = {"name": "Alice", "age": 20, "major": "Computer Science"}
        for key in student:
            print(key)  # Output: name, age, major
      

    • Iterating over values:

        student = {"name": "Alice", "age": 20, "major": "Computer Science"}
        for value in student.values():
            print(value)  # Output: Alice, 20, Computer Science
      

    • Iterating over key-value pairs:

        student = {"name": "Alice", "age": 20, "major": "Computer Science"}
        for key, value in student.items():
            print(f"{key}: {value}")
            # Output:
            # name: Alice
      

Some Dictionaries Methods:

Here are some popular methods used in dictionaries that can make your coding experience even better!

• keys(): Gives you a view of all the keys in the dictionary.

• values(): Gives you a view of all the values in the dictionary.

• items(): Gives you a view of all the (key, value) pairs as tuples.

• get(key, default): Gets the value for the given key. If the key isn't there, it returns the default value (or None if no default is given).

• update(other_dict): Adds key-value pairs from other_dict to the dictionary. It replaces values for existing keys and adds new keys.