Python学习笔记（四）

高级特性

# 高级特性# 切片（Slice）L = []n = 5 m = 20 s = 2for x in range(97,123):L.append(chr(x))print(L[n:m:s])# 索引n到索引m,不包含m(n,m可以为负),s为步长.(-1为倒数第一个元素)chr(97)#asc码转字符ord('a')#字符转asc码# 迭代# 判断对象是否可以迭代from collections import Iterableflag = isinstance(18, Iterable)print(flag) # 遍历list/tuplefor x in L:print(x)# 遍历dictionaryD = {'a':'1', 'b':'2', 'c':'3'}for value in D.values():#遍历valueprint(value)for key in D.keys():#遍历keyprint(key)for (key,value) in D.items():#遍历key,valueprint(key,value)# 列表生成式# 常规循环l1 = []for x in range(1, 11):l1.append(x)# 列表生成式l2 = [x for x in range(1,11)]l3 = [x*2+1 for x in range(1, 11) if(x%2==0)]#加判断和运算l4 = [m + n for m in 'ABC' for n in 'XYZ']#双层循环全排 l5 = [k + '=' + v for k, v in D.items()]print(l1)print(l2)print(l3)print(l4)print(l5)# 生成器(generator)# 生成式[]改为()创建一个生成器g1 = (x for x in range(1,11))for n in g1:print(n)# 函数yield 一个值创建一个生成器def sum(n):swap = 0;for x in range(n+1):swap += x*xyield swapfor x in sum(5):print(x)