Python中字典的基础用法

Python Dictionary Advanced Usage Summary

This article provides a detailed introduction to advanced usage of dictionaries in Python, which are powerful data structures for storing and accessing key-value pairs efficiently.

Merging Dictionaries

In Python 3.5 and above, dictionaries can be merged using the **kwargs syntax, and from Python 3.9 onwards, the union operator | can be used for merging.

# Python 3.5+
dict1 = {"name": "Max", "age": 28}
dict2 = {"city": "New York", "email": "max@xyz.com"}
merged_dict = {**dict1, **dict2}
# Python 3.9+
merged_dict = dict1 | dict2

Removing Elements from a Dictionary

The pop function can be used to remove an element from a dictionary and it also returns the value of the removed key.

my_dict = {"name": "Max", "age": 28}
value = my_dict.pop("age", "Key not found")
print("Removed value:", value)

Iterating Over a Dictionary

There are multiple ways to iterate over a dictionary, including iterating over keys, values, or both keys and values.

# Iterating over keys
for key in my_dict.keys():
    print(key)
# Iterating over values
for value in my_dict.values():
    print(value)
# Iterating over both keys and values
for key, value in my_dict.items():
    print(key, value)

Copying a Dictionary

When copying a dictionary, it is important to use the copy() method or the dict() function to create a true copy, not just a reference.

my_dict = {"name": "Max", "age": 28}
dict_copy = my_dict.copy()
# Or
dict_copy = dict(my_dict)

Nested Dictionaries

Dictionaries can contain any type of data as values, including another dictionary, known as nested dictionaries.

nested_dict = {"dictA": {"name": "Max", "age": 28},
               "dictB": {"name": "Alex", "age": 25}}

Accessing and Updating Nested Dictionaries

Access or update values in nested dictionaries using consecutive square brackets [] or the get() method.

nested_dict = {"dictA": {"name": "Max", "age": 28}}
# Accessing
print(nested_dict["dictA"]["name"])  # Output: Max
# Updating
nested_dict["dictA"]["age"] = 29
print(nested_dict)  # Output: {'dictA': {'name': 'Max', 'age': 29}}

Accessing Dictionary Items with get() Method

The get() method allows safe access to dictionary items, returning a default value if the key does not exist, instead of raising a KeyError exception.

original_dict = {"a": 1, "b": 2, "c": 3, "d": 4}
value1 = original_dict.get("c", "No corresponding data")
value2 = original_dict.get("e", "No corresponding data")
print(value1)  # Output: 3
print(value2)  # Output: No corresponding data

Accessing and Updating Data with setdefault() Method

The setdefault() method is similar to get() but also adds the key with the default value to the dictionary if it does not exist.

original_dict = {"a": 1, "b": 2, "c": 3, "d": 4}
original_dict.setdefault("e", 5)
print(original_dict)  # Output: {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}

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