Python列表:打工人的数据收纳神器,用它效率翻倍!

# 购物清单
shopping = ["牛奶", "面包", "鸡蛋", "牛肉"]
# 成绩单
scores = [85, 92, 78, 90, 88]
# 混搭也没问题
mixed = ["星禾", 28, True, 3.14]

fruits = ["苹果", "香蕉"]
# 末尾加一个
fruits.append("橙子")
print(fruits)  # ['苹果', '香蕉', '橙子']
# 指定位置插入
fruits.insert(1, "葡萄")
print(fruits)  # ['苹果', '葡萄', '香蕉', '橙子']
# 一次加好几个
fruits.extend(["芒果", "梨"])
print(fruits)  # ['苹果', '葡萄', '香蕉', '橙子', '芒果', '梨']

fruits = ["苹果", "香蕉", "橙子", "葡萄"]
# 按位置删
del fruits[1]          # 删除第2个
print(fruits)          # ['苹果', '橙子', '葡萄']
# 按值删（删第一个匹配的）
fruits.remove("橙子")
print(fruits)          # ['苹果', '葡萄']
# 弹出来（删掉并返回）
popped = fruits.pop()
print(popped)          # 葡萄
print(fruits)          # ['苹果']

fruits = ["苹果", "香蕉", "橙子"]
fruits[1] = "芒果"  # 直接赋值替换
print(fruits)       # ['苹果', '芒果', '橙子']

fruits = ["苹果", "香蕉", "橙子", "香蕉"]
# 索引查询
print(fruits[0])     # 苹果
print(fruits[-1])    # 橙子（倒数第一个）
# 切片查询
print(fruits[0:2])   # ['苹果', '香蕉']
# 判断存在
print("香蕉" in fruits)   # True
print("西瓜" in fruits)   # False
# 统计出现次数
print(fruits.count("香蕉"))  # 2

nums = [0, 1, 2, 3, 4, 5, 6]
print(nums[2:5])     # [2, 3, 4]  索引2到4
print(nums[:3])      # [0, 1, 2]  从头到索引2
print(nums[3:])      # [3, 4, 5, 6]  从索引3到末尾
print(nums[::2])     # [0, 2, 4, 6]  隔一个取一个
print(nums[::-1])    # [6, 5, 4, 3, 2, 1, 0]  反转

# 传统写法
squares = []
for x in range(10):
    squares.append(x ** 2)
# 列表推导式（一行搞定）
squares = [x ** 2 for x in range(10)]
print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# 筛选偶数的平方
even_squares = [x ** 2 for x in range(10) if x % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

# 把名字变成大写
names = ["alice", "bob", "charlie"]
upper_names = [name.upper() for name in names]
print(upper_names)  # ['ALICE', 'BOB', 'CHARLIE']
# 过滤无效数据
data = ["  Alice ", "Bob\n", "", "Charlie "]
clean = [s.strip() for s in data if s.strip()]
print(clean)  # ['Alice', 'Bob', 'Charlie']

fruits = ["苹果", "香蕉"]
print(fruits[5])  # IndexError！报错！

fruits = ["苹果", "香蕉"]
fruits.remove("西瓜")  # ValueError！找不到！

# 危险！
nums = [1, 2, 2, 3, 2]
for n in nums:
    if n == 2:
        nums.remove(n)  # 可能漏删！
# 安全做法
nums = [1, 2, 2, 3, 2]
nums = [n for n in nums if n != 2]  # 用列表推导式过滤

a = [1, 2, 3]
b = a            # b和a指向同一个列表！
b[0] = 99
print(a)         # [99, 2, 3]  a也被改了！
# 正确做法
a = [1, 2, 3]
b = a.copy()   # 或者 b = a[:] 或者 import copy; b = copy.deepcopy(a)

scores = [85, 92, 78, 90, 88]
# 添加成绩
scores.append(95)
print(f"平均分: {sum(scores) / len(scores):.1f}")  # 88.6
# 最高分和最低分
print(f"最高: {max(scores)}, 最低: {min(scores)}")

text = "苹果 香蕉 苹果 橙子 香蕉 苹果"
words = text.split()
# 统计词频
word_count = {}
for word in words:
    word_count[word] = word_count.get(word, 0) + 1
# 按频率排序
sorted_words = sorted(word_count.items(), key=lambda x: x[1], reverse=True)
print(sorted_words)  # [('苹果', 3), ('香蕉', 2), ('橙子', 1)]