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16 - 高级特性
学习目标: 掌握lambda, 切片, 解包, 三元表达式等
💻 代码示例
1. lambda表达式
python
# 普通函数
def add(x, y):
return x + y
# lambda(匿名函数)
add = lambda x, y: x + y
# 常用于sorted, map, filter
words = ["banana", "apple", "cherry"]
sorted_words = sorted(words, key=lambda w: len(w))
# 多个参数
points = [(1, 2), (3, 1), (5, 4)]
points.sort(key=lambda p: p[1]) # 按y坐标排序2. 高级切片
python
nums = [0, 1, 2, 3, 4, 5]
# 反转
print(nums[::-1]) # [5, 4, 3, 2, 1, 0]
# 每隔一个取一个
print(nums[::2]) # [0, 2, 4]
# 倒序每隔一个
print(nums[::-2]) # [5, 3, 1]
# 字符串反转
s = "hello"
print(s[::-1]) # olleh3. 序列解包
python
# 多变量赋值
a, b, c = 1, 2, 3
# 交换变量(Python特色!)
a, b = b, a
# *号收集剩余元素
a, *b, c = [1, 2, 3, 4, 5]
print(a) # 1
print(b) # [2, 3, 4]
print(c) # 5
# 函数返回多个值
def get_info():
return "Alice", 20, "Beijing"
name, age, city = get_info()
# 忽略某些值
x, _, z = (1, 2, 3) # 用_表示不关心的值4. 三元表达式(条件表达式)
python
# 传统if-else
if x > 0:
result = "正数"
else:
result = "非正数"
# 三元表达式(一行搞定)
result = "正数" if x > 0 else "非正数"
# 嵌套三元表达式
sign = "正" if x > 0 else ("零" if x == 0 else "负")
# 在列表推导式中使用
labels = ["偶数" if i % 2 == 0 else "奇数" for i in range(5)]5. and/or短路运算
python
# or:返回第一个真值
x = None
y = x or [] # x是None(假),返回[]
print(y) # []
# 默认值技巧
def greet(name=None):
name = name or "Guest" # name为None时使用"Guest"
print(f"Hello, {name}!")
# and:全真才返回最后一个值
result = 5 and 10 # 10
result = 0 and 10 # 0 (短路)
# 链式判断
if nums and nums[0] > 0: # 先检查非空,再访问元素
print("第一个元素是正数")6. 列表/字典快速技巧
python
# 列表去重(保持顺序)
nums = [1, 2, 2, 3, 1]
unique = list(dict.fromkeys(nums)) # [1, 2, 3]
# 字典合并(Python 3.9+)
d1 = {"a": 1, "b": 2}
d2 = {"b": 3, "c": 4}
merged = d1 | d2 # {'a': 1, 'b': 3, 'c': 4}
# 或使用**解包
merged = {**d1, **d2}
# 列表展平
matrix = [[1, 2], [3, 4], [5, 6]]
flat = [x for row in matrix for x in row]7. enumerate和zip的高级用法
python
# enumerate带起始索引
for i, val in enumerate(['a', 'b', 'c'], start=1):
print(f"第{i}个: {val}")
# zip多个列表
names = ["Alice", "Bob"]
ages = [20, 21]
cities = ["Beijing", "Shanghai"]
for name, age, city in zip(names, ages, cities):
print(f"{name}, {age}, {city}")
# zip(*list)解压
pairs = [(1, 'a'), (2, 'b'), (3, 'c')]
numbers, letters = zip(*pairs)
print(numbers) # (1, 2, 3)
print(letters) # ('a', 'b', 'c')🎯 在算法题中的应用
python
# 切片反转
def reverseString(s):
return s[::-1]
# 三元表达式
def max(a, b):
return a if a > b else b
# 序列解包交换
def reverseList(head):
prev, curr = None, head
while curr:
curr.next, prev, curr = prev, curr, curr.next
return prev
# lambda排序
intervals.sort(key=lambda x: x[0])
# and短路
if root and root.left:
...🎓 小结
✅ lambda: 匿名函数
✅ [::-1]: 反转序列
✅ a, b = b, a: 交换变量
✅ x if cond else y: 三元表达式
✅ x or default: 默认值技巧
✅ *args: 解包
下一步 : 17-递归.md
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