1. max(),min()函数的key参数应用：
快速找出众数：
>>> import random >>> r = [rnd(1,9) for _ in range(20)] >>> r [3, 3, 5, 9, 1, 7, 4, 1, 1, 9, 6, 8, 3, 9, 8, 8, 6, 4, 6, 6] >>> max(r, key=r.count) 6
找最短密码（首个匹配到的）：
>>> from random import choices, randint as rnd >>> s = ''.join((map(chr,[*range(ord('A'),ord('Z')+1),*range(ord('a'),ord('z')+1),*range(ord('0'),ord('9')+1),ord('-')]))) >>> p = [''.join(choices(s,k=rnd(3,10))) for _ in range(10)] >>> p ['fiKYKBl', 'HZjwZUGg', 'pUaKkKtrE8', '2qet35e1Q', 'is34n11F', 'Jxed96', '9K8TOE', 'sqymdfx', 'SRjuq', 'J9TBu'] >>> min(p, key=lambda x:len(x)) 'SRjuq'
位数最多、最少的整数 ：（首个匹配到的数，与最大值、最小值未必相等）
>>> from random import choices, randint as rnd >>> n = [int(''.join(map(str,choices(range(10),k=rnd(3,10))))) for _ in range(10)] >>> n [9345447, 1030757133, 8630, 293949, 497, 1206340275, 172, 950651, 983, 138] >>> max(n, key=lambda x:len(str(x))) 1030757133 >>> min(n, key=lambda x:len(str(x))) 497 >>> >>> max(n) 1206340275 >>> min(n) 138
2. 列表任意指定长度的分组：
def splitlist(lst,*group): res,lst = [],lst[:] for i in group: t = [] for _ in range(i): if lst: t.append(lst.pop(0)) else: break if t: res.append(t) if lst: res.append(lst) return res a = [1,2,3,4,5,6,7,10,11,12,20,21,23] print(splitlist(a,8,4,2,1)) # [[1, 2, 3, 4, 5, 6, 7, 10], [11, 12, 20, 21], [23]] print(splitlist(a,7,3,2,1)) # [[1, 2, 3, 4, 5, 6, 7], [10, 11, 12], [20, 21], [23]] print(splitlist(a,7,3,2,2)) # [[1, 2, 3, 4, 5, 6, 7], [10, 11, 12], [20, 21], [23]] print(splitlist(a,7,3,2)) # [[1, 2, 3, 4, 5, 6, 7], [10, 11, 12], [20, 21], [23]] print(splitlist(a,7,3)) # [[1, 2, 3, 4, 5, 6, 7], [10, 11, 12], [20, 21, 23]] print(splitlist(a,7,2,2,5)) # [[1, 2, 3, 4, 5, 6, 7], [10, 11], [12, 20], [21, 23]]
3. 用numpy解多元一次方程组：
import numpy as np A = [[1,-2,1],[0,2,-8],[-4,5,9]] # 系数矩阵 B = [0,8,-9] # 常数矩阵 x,y,z = np.linalg.inv(A).dot(B) # 求方程组的解 print(f'x={x}, y={y}, z={z}') # 默认它有且只有一组解，不展开讨论
4. 应用字典同时返回两数的和差积商余
def exp(a,b): choice = { 1: lambda x, y: x + y, 2: lambda x, y: x - y, 3: lambda x, y: x * y, 4: lambda x, y: x // y, 5: lambda x, y: x % y } return tuple(choice[i+1](a,b) for i in range(5)) print(exp(8,3)) # (11, 5, 24, 2, 2) print(exp(5,6)[2]) # 30
5. 多种方法取出某字母开头的元素
>>> s = ['foot','head','Face','Hair','nose','Mouth','finger','ear'] >>> [w for w in s if w[0].lower()=='f'] ['foot', 'Face', 'finger'] >>> [w for w in s if w[0] in ('f','F')] ['foot', 'Face', 'finger'] >>> [w for w in s if w.startswith(('F','f'))] ['foot', 'Face', 'finger']
6. 输入一个整数，输错不会异常退出
1. n = '' 2. while not n.isnumeric(): n = input('输入一个非负整数：') 3. n = int(n)
n = '' while not (n.isnumeric() or len(n) and n[0]=='-' and n[1:].isnumeric()): n = input('输入一个整数：') n = int(n)
