Python Dictionaries and Sets: Organize Named Data and Remove Duplicates

When we start learning Python, lists are often one of the first data structures we use: student = ["Laura", 24, "Medellín"] Enter fullscreen mode Exit fullscreen mode This works, but what does each position represent? We need to remember that: Position 0 contains the name. Position 1 contains the age. Position 2 contains the city. A dictionary provides a clearer alternative because every value is identified by a descriptive key. Creating a dictionary A dictionary stores information as key-value pairs: student = { "name": "Laura", "age": 24, "city": "Medellín" } Enter fullscreen mode Exit fullscreen mode Instead of asking for the value at position 0, we can ask directly for the value associated with "name": print(student["name"]) Enter fullscreen mode Exit fullscreen mode Output: Laura Enter fullscreen mode Exit fullscreen mode A useful way to remember the difference is: A list position tells you where a value is. A dictionary key tells you what the value means. Updating and adding information Python dictionaries are mutable, so their content can change after creation. To update an existing value: product = { "name": "Keyboard", "price": 120000 } product["price"] = 110000 Enter fullscreen mode Exit fullscreen mode To add a new key-value pair, use the same syntax with a key that does not exist yet: product["available"] = True Enter fullscreen mode Exit fullscreen mode The resulting dictionary is: { "name": "Keyboard", "price": 110000, "available": True } Enter fullscreen mode Exit fullscreen mode Safely reading values with get() Using square brackets requires the key to exist: print(student["email"]) Enter fullscreen mode Exit fullscreen mode If "email" is missing, Python raises a KeyError. The get() method provides a safer alternative: print(student.get("email")) Enter fullscreen mode Exit fullscreen mode It returns None when the key is missing. You can also define a default value: print(student.get("email", "Not registered")) Enter fullscreen mode Exit fullscreen mode Output: Not registered Enter fullscreen mode Exit fullscreen mode To check whether a key exists, use the in operator: if "city" in student: print(student["city"]) Enter fullscreen mode Exit fullscreen mode Keys, values, and pairs Python provides three useful dictionary methods: course = { "name": "Python Basics", "duration": "4 weeks", "format": "Online" } print(course.keys()) print(course.values()) print(course.items()) Enter fullscreen mode Exit fullscreen mode They provide different views of the same information: keys() returns the keys. values() returns the stored values. items() returns complete key-value pairs. Looping through a dictionary The items() method is especially useful when working with a for loop: capitals = { "Colombia": "Bogotá", "Peru": "Lima", "Argentina": "Buenos Aires" } for country, capital in capitals.items(): print(f"{country}: {capital}") Enter fullscreen mode Exit fullscreen mode Output: Colombia: Bogotá Peru: Lima Argentina: Buenos Aires Enter fullscreen mode Exit fullscreen mode During every iteration, Python assigns the current key to country and its associated value to capital. What is a set? A set is a collection that stores unique values. Consider this list: languages = ["Python", "Rust", "Python", "JavaScript", "Rust"] Enter fullscreen mode Exit fullscreen mode We can remove repeated values by converting it into a set: unique_languages = set(languages) print(unique_languages) Enter fullscreen mode Exit fullscreen mode The set keeps only one occurrence of each language. Sets are useful when you need to: Remove duplicate values. Check whether a value is present. Compare groups of elements. Work with unique categories or identifiers. Unlike lists, sets do not support indexes or slicing. An important detail Empty braces create an empty dictionary: empty_dictionary = {} Enter fullscreen mode Exit fullscreen mode To create an empty set, use set(): empty_set = set() Enter fullscreen mode Exit fullscreen mode This is a common source of confusion for Python beginners. Which structure should you choose? Use a list when position and order are important. Use a dictionary when every value should have a descriptive name. Use a set when you need unique values and repetitions do not matter. Understanding this distinction makes programs easier to read, maintain, and extend. The original Spanish guide includes a step-by-step explanation with additional examples: https://tucodigocotidiano.yarumaltech.com/leer_guias/diccionarios-y-conjuntos-datos-con-nombre-y-sin-duplicados/ What was more confusing when you first learned Python: dictionaries or sets?