Day16: python生产列表的使用方法

数据再运算

a = range(0,15)
b = [_**2 for _ in a]
c = [str(_) for _ in a]
print(b)
print(c)

output: 
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196]
['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14']

就是说用好循环，变量值怎么赋值  掌握这种小技巧

一串随机数

#生成 10 个 0 到 1 的随机浮点数，保留小数点后两位
from random import random
a = [round(random(),2) for _ in range(10)]
print(a)
#生成 10 个 0 到 10 的满足均匀分布的浮点数，保留小数点后3位：
from random import uniform
b = [round(uniform(0,10),3) for _ in range(10)]
print(b)

output:
[0.53, 0.14, 0.0, 0.42, 0.27, 0.87, 0.89, 0.28, 0.5, 0.65]
[2.206, 5.056, 8.73, 8.816, 2.416, 7.271, 2.327, 8.125, 8.961, 2.768]

if 和嵌套 for

#对一个列表里面的数据筛选，只计算 [0,11) 中3的倍数
a = range(15)
b = [x**2 for x in a if x%3==0]
print(b)
# for 嵌套 for .一行代码生成 99 乘法表的所有 45 个元素
c = [i*j for i in range(10) for j in range(1,i+1)] 
print(c)

output:
[0, 9, 36, 81, 144]
[1, 2, 4, 3, 6, 9, 4, 8, 12, 16, 5, 10, 15, 20, 25, 6, 12, 18, 24, 30, 36, 7, 14, 21, 28, 35, 42, 49, 8, 16, 24, 32, 40, 48, 56, 64, 9, 18, 27, 36, 45, 54, 63, 72, 81]

zip 和列表

# zip 和列表
a= range(4)
b = ['a','b','c','d','e']
c = [str(y) + str(x) for x, y in zip(a,b)]
print(c)
zip(a,b)

output:
['a0', 'b1', 'c2', 'd3']
<zip at 0x6fffe0ab948>

zip(a, b)用法:元素对

打印键值对

#以列表形式 打印键值对 
a = {'a':1,'b':2,'c':3}
b = [k+ '=' + str(v) for k, v in a.items()]
print(b)

output:
['a=1', 'b=2', 'c=3']

文件列表

import os
# 设置目标路径
dirs = [d for d in os.listdir('/home/sage/PYTHON60DAYS') if os.path.isdir(d)]#找文件夹
files = [d for d in os.listdir('/home/sage/PYTHON60DAYS') if os.path.isfile(d)]#找文件
print(dirs)
print(files)

output:
['.ipynb_checkpoints']
['day121314.ipynb', 'day15.ipynb', 'day16.ipynb', 'day5-Copy1.ipynb', 'day5.ipynb']

转为小写

a = ['Hello', 'World', '2019Python']
b = [_.lower() for _ in a]
print(b)

output:
['hello', 'world', '2019python']

但是如果由于列表中元素并不是都是str,比如说有数值类型，就会报错，要么就是先转化为str,要么就是使用sinstance，判断元素是否为 str 类型，如果是，再调用 lower 做转化：

a = ['Hello', 'World', '2019Python', 2020, 'asdaASD']
c = [w.lower() for w in a if isinstance(w,str) ]
print(c)

output:
['hello', 'world', '2019python', 'asdaasd']

上面显然不是str类型就不在转化出来的[]中了

保留唯一值

# 保留唯一值，那些列表中只出现过一次的值  list.count(item)
def filter_non_unique(lst):
    return [item for item in lst if lst.count(item) == 1]
filter_non_unique([1, 2, 2, 3, 4, 4, 5])

output:
[1, 3, 5]

筛选分组

#筛选分组  利用某种属性进行分组
def bifurcate(lst, filter):
    return [
        [x for i,x in enumerate(lst) if filter[i] == True],
        [x for i,x in enumerate(lst) if filter[i] == False]
    ]
bifurcate(['beep', 'boop', 'foo', 'bar'], [True, True, False, True])

output：
[['beep', 'boop', 'bar'], ['foo']]

函数分组

#利用函数运行结果分组  fn是函数  lambda x: x[0] == 'u'就是一个函数，返回true or false 
def bifurcate_by(lst, fn):
    return [
        [x for x in lst if fn(x)],
        [x for x in lst if not fn(x)]
    ]
bifurcate_by(['Python3', 'up', 'users', 'people'], lambda x: x[0] == 'u')

output:
[['up', 'users'], ['Python3', 'people']]

差集

#差集 a b 为lst
def difference(a, b):
    _a, _b =set(a),set(b)
    return [item for item in _a if item not in _b]#返回a中那些没有出现在b中的元素
difference([1,1,2,3,3,5,15], [1, 2, 4,15])

output:
[3, 5]