Python 匿名函数 (Lambda)

大家好！今天我们来聊聊匿名函数 (lambda)。匿名函数在Python中是一种简洁的函数定义方式。匿名函数适用于简单的操作，不需要命名。它使用lambda关键字创建，语法为：lambda 参数: 表达式。 lambda经常出现在map, filter, reduce等高阶函数中。

在示例中，我们使用lambda对字典列表按年龄排序。同时，我们用lambda筛选出年龄大于25岁的人。还可以结合多个条件，如年龄和城市进行筛选。在示例中，我们使用lambda和字典解包操作符(**x)。这允许我们基于原字典创建新字典，并将年龄翻倍。

lambda的优点是代码简洁，适合短小的逻辑。但缺点是对于复杂逻辑可能会降低代码可读性。因此，建议仅在简单场景中使用匿名函数。

希望这个简单的例子能帮助你理解Python的lambda！

代码示例

people = [
    {"name": "Alice", 
     "age": 25, 
     "city": "Beijing"},
    {"name": "Bob", 
     "age": 30, 
     "city": "Shanghai"},
    {"name": "Cathy", 
     "age": 20, 
     "city": "Beijing"},
    {"name": "David", 
     "age": 35, 
     "city": "Guangzhou"}
]

# Sort by age
sorted_by_age = sorted(
    people, 
    key=lambda x: x["age"]
)

# Filter adults
filtered_adults = list(
    filter(
        lambda x: x["age"] > 25, 
        people
    )
)

# Filter by age and city
filtered_by_age_and_city = list(
    filter(
        lambda x: x["age"] > 25 
        and x["city"] == "Beijing", 
        people
    )
)

# Advanced: Lambda in a 
# higher-order function, 
# simplified
doubled_ages = list(
    map(
        lambda x: {
            **x, 
            "age": x["age"] * 2
        }, 
        people
    )
)

# Function to print list 
# with title
def print_list(title, items):
    print(title)
    for p in items:
        print(f"{p['name']}: "
              f"{p['age']} years old, "
              f"{p['city']}")

# Print all results at the 
# end
print_list(
    "Sorted by age:", 
    sorted_by_age
)
print_list(
    "\nAdults list:", 
    filtered_adults
)
print_list(
    "\nAdults from Beijing:", 
    filtered_by_age_and_city
)
print_list(
    "\nDoubled ages:", 
    doubled_ages
)

Python 匿名函数 (Lambda)

代码示例​

代码示例