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{"managingGroups":{},"author":"FolkN","updateTime":1712374874000,"title":"Dictionary notes","dislikeCnt":0,"content":"\n### What is a Dictionary?\nA dictionary in Python is a collection of key-value pairs. Each key is unique within a dictionary, and it maps to a corresponding value. Dictionaries are unordered, meaning the order of elements is not guaranteed.\n\n### Creating a Dictionary\nYou can create a dictionary using curly braces `{}` and specifying key-value pairs, separated by colons `:`. For example:\n```python\nmy_dict \u003d {\u0027name\u0027: \u0027John\u0027, \u0027age\u0027: 30, \u0027city\u0027: \u0027New York\u0027}\n```\n\n### Accessing Values\nYou can access the value associated with a key using square brackets `[]`. For example:\n```python\nprint(my_dict[\u0027name\u0027]) # Output: John\n```\n\n### Adding and Modifying Elements\nYou can add new key-value pairs or modify existing ones:\n```python\nmy_dict[\u0027email\u0027] \u003d \u0027john@example.com\u0027 # Adding a new key-value pair\nmy_dict[\u0027age\u0027] \u003d 31 # Modifying an existing value\n```\n\n### Dictionary Functions and Methods\n- `len(dictionary)`: Returns the number of key-value pairs in the dictionary.\n- `dict.keys()`: Returns a view object that displays a list of all the keys in the dictionary.\n- `dict.values()`: Returns a view object that displays a list of all the values in the dictionary.\n- `dict.items()`: Returns a view object that displays a list of key-value tuples in the dictionary.\n- `dict.get(key)`: Returns the value associated with the specified key. If the key does not exist, it returns None.\n- `dict.pop(key)`: Removes the specified key and its associated value from the dictionary.\n- `dict.popitem()`: Removes and returns an arbitrary key-value pair from the dictionary.\n- `dict.clear()`: Removes all items from the dictionary.\n- `dict.copy()`: Returns a shallow copy of the dictionary.\n\n### Use Cases\nDictionaries are versatile and can be used for various purposes such as:\n- Storing settings and configurations.\n- Representing JSON data.\n- Counting occurrences of elements in a list.\n- Mapping unique identifiers to objects in a program.\n\n### Type of Problems to Use Dictionaries\nDictionaries are particularly useful in scenarios where you need to map keys to values for efficient lookup and retrieval. Some common problems where dictionaries excel include:\n- Word frequency counting in text processing.\n- Storing user information in a web application.\n- Implementing a cache for expensive function calls.\n- Creating lookup tables for efficient algorithmic solutions.\n\ndictionaries in Python are powerful data structures for mapping keys to values, providing fast access and manipulation capabilities, making them suitable for a wide range of programming tasks.","threadId":188785,"likeCnt":5,"createTime":1712374874000,"isWorkbook":false,"viewCnt":218,"openness":2,"fav":false,"id":4821,"trustable":false}