列表推导式、字典推导式和集合推导式

1.列表推导式：生成新的列表   

[expression for item in iterable]

   numbers = [1, 2, 3, 4, 5]
   squares = [x**2 for x in numbers]
   print(squares)  # 输出: [1, 4, 9, 16, 25]

 

2.字典推导式：生成新的字典

 {key_expression: value_expression for item in iterable}

   numbers = [1, 2, 3, 4, 5]
   squares_dict = {x: x**2 for x in numbers}
   print(squares_dict)  # 输出: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
   

 

3.集合推导式：生成新的集合

{expression for item in iterable}

   numbers = [1, 2, 3, 4, 5, 1, 2, 3]
   unique_numbers = {x for x in numbers}
   print(unique_numbers)  # 输出: {1, 2, 3, 4, 5}
   

 

4.条件过滤：在推导式中添加条件

[expression for item in iterable if condition]

   numbers = [1, 2, 3, 4, 5]
   even_numbers = [x for x in numbers if x % 2 == 0]
   print(even_numbers)  # 输出: [2, 4]
   

 

5.嵌套推导式：在推导式中嵌套另一个推导式

[expression for outer_item in outer_iterable for inner_item in inner_iterable]

   matrix = [[1, 2], [3, 4], [5, 6]]
   flat_list = [item for row in matrix for item in row]
   print(flat_list)  # 输出: [1, 2, 3, 4, 5, 6]