最简形式：[expression for item in list]

"""
求1-5 的平方
"""
print([i ** 2 for i in range(1, 6)])
# 输出结果：[1, 4, 9, 16, 25]

word_list = ["I", "love", "China"]
print([item.title() for item in word_list])
# 输出结果：['I', 'Love', "China"]

过滤条件形式 [expression for item in list if conditional]

如果只有if， 则if在for循环后边；如果有if...else, 则if...else在for循环前边

list_val = []
for i in range(1, 21):
    if i % 2 ==0:
        list_val.append(i)
print(list_val)

# 列表解析式
print([i for i in range(1, 21) if i % 2 == 0])
# 运行结果：[2, 4, 6, 8, 10, 12, 14, 16, 18]

names = ['Elsa', 'John', 'Jessie']
new_list = []
for item in names:
    if len(item) > 4:
        new_list.append(item.upper())
    else:
        new_list.append(item.lower())
print(new_list)

# 列表解析式
print([item.upper() if len(item) >4 else item.lower() for item in names])

# 运行结果：['elsa', 'john', 'JESSIE']

循环嵌套形式[expression for i in list1 for j in list2]

list_val = []
for i in range(1,3):
    for j in range(1,3):
        list_val.append(f'{i} + {j}')
print(list_val)

# 列表解析式
print([f'{i} + {j}' for i in range(1, 3) for j in range(1, 3)])
# 运行结果:['1 + 1', '1 + 2', '2 + 1', '2 + 2']