Dictionaries

Dictionaries

1. Definition

   • A data structure
     • Stores key-value pairs
     • Mutable and unordered

2. Characteristics

   • Keys
     • Unique within a dictionary
     • Immutable types (e.g., strings, numbers, tuples)
   • Values
     • Can be of any data type
     • Can be duplicated

3. Creating a Dictionary

   • Using curly braces
     • Syntax: {key1: value1, key2: value2}
   • Using the dict() constructor
     • Syntax: dict(key1=value1, key2=value2)

4. Accessing Elements

   • Using keys
     • Syntax: dict_name[key]
   • Using get() method
     • Syntax: dict_name.get(key)

5. Modifying a Dictionary

   • Adding new key-value pairs
     • Syntax: dict_name[new_key] = new_value
   • Updating existing key-value pairs
     • Syntax: dict_name[existing_key] = new_value

6. Built-in functions

   • len()
     • Function that returns the number of items
     • Counts key-value pairs
     • Example: len(my_dict)
   • dict()
     • Create dictionary objects
   • keys()
     • Retrieves keys from a dictionary
     • Syntax: my_dict.keys()
   • values()
     • Retrieves values from the dictionary
     • Syntax: my_dict.values()
   • items()
     • Retrieves key-value pairs
     • Syntax: dict.items()
   • update()
     • Method to update dictionaries
       • Adds new key-value pairs
       • Updates existing key values
       • Syntax: dict1.update(dict2)
   • get()
     • Method for retrieving values
     • Syntax: dict.get(key, default)
   • del
     • Removes a specified item;
       • Syntax: del dictionary[key];
   • clear
     • Removes all items
     • Empties the dictionary
     • Example: my_dict.clear()
   • fromkeys()
     • A method for creating a new dictionary.
       • Examples
         • Creating a dictionary with specified keys.
           • Example: `dict.fromkeys(['a', 'b', 'c'])`
         • Creating a dictionary with specified keys and a default value.
           • Example: `dict.fromkeys(['x', 'y', 'z'], 0)`
   • copy()
     • Creates a shallow copy of a dictionary
       • dict.copy() method
   • pop()
     • Remove an item
       • Based on the provided key
         • Syntax: dict.pop(key[, default])
   • popitem()
     • Method to remove and return an arbitrary (last) key-value pair
   • setdefault()
     • Retrieve value if key exists
       • If key not present, add key with default value
         • Syntax: dict.setdefault(key, default=None)
   • max(), min()
     • max()
       • Returns the largest item;
     • min()
       • Returns the smallest item;
   • sorted()
     • Returns a sorted list of the dictionary keys
       • Example: sorted(d)