推导式、生成器与切片

一、实验要求

1.理解并掌握序列中的常用操作。
2.理解并掌握推导式、切片等用法并能解决实际问题。

二、实验内容

1，编写程序，测试字符的出现频率。

    #use dict method1
data = ['a','2',2,3,6,'2','b',4,7,2,'6','d',6,'a','z']
frequences=dict()
for item in data:
    if item in frequences:
        frequences[item] += 1
    else:
        frequences[item] = 1
print frequences

#use dict method2
frequences = dict()
for item in data:
    frequences[item] = frequences.get(item,0) + 1
print frequences

#use defaultdict
from collections import defaultdict
frequences = defaultdict(int)
for item in data:
    frequences[item] += 1
print frequences.items()

#use set and list type
count_set = set(data)
count_list = []
for item in count_set:
    count_list.append((item,data.count(item)))
print count_list

#use collections.Counter
from collections import Counter
frequences = Counter(data)
print frequences.items()
print list(frequences.elements())    #list all the elements
print frequences.most_common(3)       

2， 编写程序求100以内的所有奇数的和。

sum = 0
for i in range(1,100,2):
sum = sum + i 
print(sum)

3，编写程序，生成包含30个随机整数的列表，然后对偶数下标的元素降序排列，奇数下标的元素不变。

import random
x = [random.randint(0,100) for i in range(30)]
#print(x) 打印x看看原列表
y = x[::2]
#print(y) 打印偶数坐标
y.sort(reverse=True)
x[::2] = y
print(x)