Python 中的列表推导式
列表推导式是一种 Python 构造，可减少生成新列表或过滤现有列表所需的代码行。列表推导式包含在方括号内，它由一个表达式、一个或多个 for 循环和一个用于过滤生成的列表的可选条件组成。
列表推导式使用以下语法：
new_list = [expression(item) for item in iterable if condition]翻译翻译就是：
new_list = []for item in iterable: if condition: new_list.append(expression(item))简单用法
最原始的1到10
numbers = [x for x in range(1,11)]print(numbers)>>> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]乘个2
numbers = [2*x for x in range(1,11)]print(numbers)>>> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]只要偶数
numbers = [x for x in range(1,11) if x%2==0]print(numbers)>>> [2, 4, 6, 8, 10]来个等差数列
numbers = [2*x-1 for x in range(1,11)]print(numbers)>>> [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]来个二维数组
numbers = [[x, x**2] for x in range(2,7)]print(numbers)>>> [[2, 4], [3, 9], [4, 16], [5, 25], [6, 36]]添加多个条件
只要一个范围内
numbers = [2*x for x in range(1,11) if x>2 and x<5]print(numbers)>>> [6, 8]要添加 else 条件，我们必须重新排列列表理解元素的顺序。一个三元表达式的顺序
我们必须将条件移动到 for 关键字之前，以便在不满足 if 条件时返回一个不同于 2*x 的值。
# 如果 x 的值介于2和5之间，则列表推导式返回 2*x，否则返回 3*x。numbers = [2*x if x > 2 and x < 5 else 3*x for x in range(10)]print(numbers)>>> [0, 3, 6, 6, 8, 15, 18, 21, 24, 27]如果条件在多一点
numbers = []for x in range(10): if x > 2 and x < 5: numbers.append(2*x) elif x <=2: numbers.append(3*x) else: numbers.append(4*x)print(numbers)>>> [0, 3, 6, 6, 8, 20, 24, 28, 32, 36]numbers = [2*x if x > 2 and x < 5 else 3*x if x <=2 else 4*x for x in range(10)]print(numbers)>>> [0, 3, 6, 6, 8, 20, 24, 28, 32, 36]多个列表使用
与 zip 函数一起使用的列表推导返回一个元组列表，其中第 n 个元组包含每个列表的第 n 个元素。
cities = ['Rome', 'Warsaw', 'London']countries = ['Italy', 'Poland', 'United Kingdom']abc = [(city, country) for city, country in zip(cities, countries)]print(abc)>>> [('Rome', 'Italy'), ('Warsaw', 'Poland'), ('London', 'United Kingdom')]cities = ['Rome', 'Warsaw', 'London']countries = ['Italy', 'Poland', 'United Kingdom']languages = ['Italian', 'Polish', 'English']abc = [(city, country, language) for city, country, language in zip(cities, countries, languages)]print(abc)>>> [('Rome', 'Italy', 'Italian'), ('Warsaw', 'Poland', 'Polish'), ('London', 'United Kingdom', 'English')]下面演示了两种不同的加法。挨个加一遍，，对应加，，
a = [2, 3, 4, 5]b = [12, 13, 14, 15]abc = [x+y for x in a for y in b]print(abc)>>> [14, 15, 16, 17, 15, 16, 17, 18, 16, 17, 18, 19, 17, 18, 19, 20]a = [2, 3, 4, 5]b = [12, 13, 14, 15]abc = [x+y for x,y in zip(a,b)]print(abc)>>> [14, 16, 18, 20]三个也是一样的
a = [2, 3]b = [12, 13]c = [22, 23]abc = [x+y+z for x in a for y in b for z in c]print(abc)>>> [36, 37, 37, 38, 37, 38, 38, 39]a = [2, 3, 4, 5]b = [12, 13, 14, 15]c = [22, 23, 24, 25]abc = [x+y+z for x,y,z in zip(a,b,c)]print(abc)>>> [36, 39, 42, 45]替换 Reduce 和 Lambda
reduce 函数返回总和
from functools import reducenumbers = [3, 6, 8, 23]print(reduce(lambda a,b: a+b, numbers))>>> 40修改一下
print(sum([number for number in numbers]))>>> 40嵌套列表推导式
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]for row in matrix: for item in row: item *= 2print(matrix)>>> [[2, 4, 6], [8, 10, 12], [14, 16, 18]]简单地来个转换
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]matrix = [[item*2 for item in row] for row in matrix]print(matrix)>>> [[2, 4, 6], [8, 10, 12], [14, 16, 18]]来源地址：https://blog.csdn.net/qq_55342245/article/details/125721713
