Python中字典的基础用法

125 2024-10-26

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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}