声明式编程题

声明式编程练习题：

1、将names=['egon','alex_sb','wupeiqi','yuanhao']中的名字全部变大写

names = ['egon', 'alex_sb', 'wupeiqi', 'yuanhao']
# 方式一:手动实现
new_names = []
for line in names:
    new_names.append(line.swapcase())
print(new_names)

# 方式二:列表生成式
new_names = [line.swapcase() for line in names]
print(new_names)

# 方式三:map+匿名函数
res = map(lambda line: line.swapcase(), names)
print(list(res))

names = [name.upper() for name in names]
print(names)


2、将names=['egon','alex_sb','wupeiqi','yuanhao']中以sb结尾的名字过滤掉，然后保存剩下的名字长度

names = ['egon', 'alex_sb', 'wupeiqi', 'yuanhao']

new_names = []
for line in names:
    if not line.endswith('sb'):
        new_names.append(line)
print(new_names)

new_names = [len(line) for line in names if not line.endswith('sb')]
print(new_names)

res = filter(lambda line: not line.endswith('sb'), names)
print(list(res))

3、求文件a.txt中最长的行的长度（长度按字符个数算，需要使用max函数）

file = []
with open('a.txt', 'rt', encoding='utf-8')as f:
    for line in f:
        res = f.read()
        # print(res)
        res = res.split('\n')
        file.append(res)
print(file)


def funcs(x):
    return len(x)


res = max(file, key=funcs)
print(res)
res2 = max(res, key=funcs)
print(len(res2))

print(max(len(line) for line in f))

4、求文件a.txt中总共包含的字符个数？思考为何在第一次之后的n次sum求和得到的结果为0？（需要使用sum函数）

with open('a.txt', 'rt', encoding='utf-8')as f:
    print(sum(len(line) for line in f))
print(sum(len(line) for line in f))  # 求包换换行符在内的文件所有的字符数，为何得到的值为0?

5、思考题

with open('a.txt') as f:
    g = (len(line) for line in f)
print(sum(g))  # 为何报错？

with open('a.txt') as f:
    print(sum(len(line) for line in f))
print(sum(g))  # 为何报错？(len(line) for line in f)时循环多个值

6、文件shopping.txt内容如下

    mac,20000,3
    lenovo,3000,10
    tesla,1000000,10
    chicken,200,1
    求总共花了多少钱？
    打印出所有商品的信息，格式为[{'name':'xxx','price':333,'count':3},...]
    求单价大于10000的商品信息,格式同上

with open('shopping.txt', 'rt', encoding='utf-8') as f:
    info = [line.strip('\n').split(',') for line in f]
    print(info)
    cost = sum(float(unit_price) * int(count) for _, unit_price, count in info)
    print(cost)

with open('shopping.txt', 'rt', encoding='utf-8') as f:
    # for line in f:
    #     print(line)
    info = [{'name': line.strip('\n').split(',')[0],
             'price': int(line.strip('\n').split(',')[1]),
             'count': int(line.strip('\n').split(',')[2])} for line in f]
    print(info)

with open('shopping.txt', encoding='utf-8') as f:
    info = [{'name': line.strip('\n').split(',')[0],
             'price': int(line.strip('\n').split(',')[1]),
             'count': int(line.strip('\n').split(',')[2])} for line in f if int(line.strip('\n').split(',')[1]) > 10000]
    print(info)