[expression for item in iterable if condition]

# 傳統(tǒng)方式
squares = []
for x in range(10):
    squares.append(x**2)

# 列表推導(dǎo)式
squares = [x**2 for x in range(10)]
print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# 只保留偶數(shù)平方
even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

# 使用條件表達(dá)式
results = ["偶數(shù)" if x % 2 == 0 else "奇數(shù)" for x in range(5)]
print(results)  # ['偶數(shù)', '奇數(shù)', '偶數(shù)', '奇數(shù)', '偶數(shù)']

# 生成所有可能的坐標(biāo)對(duì)
coordinates = [(x, y) for x in range(3) for y in range(3)]
print(coordinates)  # [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

{key_expression: value_expression for item in iterable if condition}

# 創(chuàng)建數(shù)字到其平方的映射
squares_dict = {x: x**2 for x in range(5)}
print(squares_dict)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# 反轉(zhuǎn)字典的鍵和值
original = {'a': 1, 'b': 2, 'c': 3}
reversed_dict = {v: k for k, v in original.items()}
print(reversed_dict)  # {1: 'a', 2: 'b', 3: 'c'}

# 帶條件的字典推導(dǎo)式
even_squares = {x: x**2 for x in range(10) if x % 2 == 0}
print(even_squares)  # {0: 0, 2: 4, 4: 16, 6: 36, 8: 64}

{expression for item in iterable if condition}

# 從列表中創(chuàng)建不重復(fù)的平方數(shù)集合
numbers = [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]
unique_squares = {x**2 for x in numbers}
print(unique_squares)  # {16, 1, 9, 4}

# 帶條件的集合推導(dǎo)式
even_squares = {x**2 for x in range(10) if x % 2 == 0}
print(even_squares)  # {0, 64, 4, 36, 16}

(expression for item in iterable if condition)

# 創(chuàng)建生成器
squares_gen = (x**2 for x in range(10))

# 使用生成器
print(next(squares_gen))  # 0
print(next(squares_gen))  # 1

# 可以轉(zhuǎn)換為列表
print(list(squares_gen))  # [4, 9, 16, 25, 36, 49, 64, 81]

# 在函數(shù)中使用
total = sum(x**2 for x in range(10))
print(total)  # 285

# 二維列表展平
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flattened = [num for row in matrix for num in row]
print(flattened)  # [1, 2, 3, 4, 5, 6, 7, 8, 9]

# 轉(zhuǎn)置矩陣
transposed = [[row[i] for row in matrix] for i in range(3)]
print(transposed)  # [[1, 4, 7], [2, 5, 8], [3, 6, 9]]

# 多個(gè)條件
numbers = [x for x in range(20) if x % 2 == 0 if x % 3 == 0]
print(numbers)  # [0, 6, 12, 18]

# 復(fù)雜的條件表達(dá)式
categorized = ["大偶數(shù)" if x > 5 and x % 2 == 0 else 
               "小偶數(shù)" if x % 2 == 0 else 
               "大奇數(shù)" if x > 5 else 
               "小奇數(shù)" for x in range(10)]
print(categorized)

import timeit
# 測(cè)試列表推導(dǎo)式性能
list_comp_time = timeit.timeit('[x**2 for x in range(1000)]', number=10000)
loop_time = timeit.timeit('''
result = []
for x in range(1000):
    result.append(x**2)
''', number=10000)

print(f"列表推導(dǎo)式: {list_comp_time:.3f}秒")
print(f"傳統(tǒng)循環(huán): {loop_time:.3f}秒")

# 可讀性好的推導(dǎo)式
good_example = [x**2 for x in range(10) if x % 2 == 0]

# 過(guò)于復(fù)雜的推導(dǎo)式（不推薦）
bad_example = [[x*y for y in range(10) if y % 2 == 0] for x in range(10) if x % 3 == 0]

# 從字符串中提取數(shù)字并轉(zhuǎn)換為整數(shù)
data = ["價(jià)格: 100元", "重量: 2.5kg", "數(shù)量: 15個(gè)"]
numbers = [float(''.join(filter(str.isdigit, item))) for item in data]
print(numbers)  # [100.0, 25.0, 15.0]

# 讀取文件并處理行
with open('data.txt', 'r') as file:
    lines = [line.strip().upper() for line in file if line.strip()]

# 從API響應(yīng)中提取特定信息
api_response = [
    {'name': 'Alice', 'age': 25, 'active': True},
    {'name': 'Bob', 'age': 30, 'active': False},
    {'name': 'Charlie', 'age': 35, 'active': True}
]

active_users = [user['name'] for user in api_response if user['active']]
print(active_users)  # ['Alice', 'Charlie']

# 可讀性更好的復(fù)雜推導(dǎo)式
result = [
    (x, y, z)
    for x in range(10)
    for y in range(10)
    for z in range(10)
    if x + y + z > 15
    and x % 2 == 0
    and y % 2 != 0
]

print(result)