python(19)- 列表生成式和生成器表达式练习Ⅰ
2024-08-27 06:51:16
列表表达式
程序一:
常规写法:
egg_list=[] for i in range(100):
egg_list.append('egg%s' %i)
print(egg_list)
列表表达式写法:
l=['egg%s' %i for i in range(100) if i > 0] #列表写法:[命令+循环语句]。'egg%s' %i 这句话在列表中,所以不用append命令写入列表中
print(l)
程序二:
常规写法:
l=[1,2,3,4]
s='hello'
l1=[]
for num in l:
for s1 in s:
t=(num,s1)
l1.append(t)
print(l1)
列表表达式写法:
l1=[(num,s1) for num in l if num > 0 for s1 in s] #if num >0 这句判断可以去掉
print(l1)
程序三:
常规写法:
import os
#查看xuyaping文件夹所有的绝对路径
g=os.walk('F:\\xuyaping')
file_path_list=[]
for i in g:
# print(i)
for j in i[-1]:
file_path_list.append('%s\\%s' %(i[0],j)) print(file_path_list)
列表表达式写法:
g=os.walk('F:\\xuyaping')
l1=['%s\\%s' %(i[0],j) for i in g for j in i[-1]]
print(l1)
生成器表达式
相比列表表达式,只不过将[]换成了(),更加省内存。
程序一:
列表表达式写法:
l=['egg%s' %i for i in range(10000)]
print(l)
生成器表达式写法:
g=l=('egg%s' %i for i in range(10000))
print(g)
print(next(g))
print(next(g))
for i in g:
print(i)
程序二:
常规写法:
f=open('a.txt')
l=[]
f.seek(0) #光标移动到文档首行首位
for line in f:
line=line.strip()
l.append(line)
print(l)
列表表达式写法:
f=open('a.txt')
f.seek(0)
l1=[line.strip() for line in f]
print(l1)
生成器表达式写法:
f=open('a.txt')
f.seek(0)
g=(line.strip() for line in f)
print(g)
print(next(g))
程序三:
生成器表达式写法:
f=open('a.txt')
g=(line.strip() for line in f) #g为迭代器 l=list(g) #list(可迭代对象),迭代取出g中的所有内容
print(l)
---->['asdfasdfasdfasdfasdf', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '123123123123', '', 'asdfasdfasdfasdf'] nums_g=(i for i in range(3)) # print(sum([1,2,3,4]))
print(sum(nums_g)) #sum(可迭代对象),迭代将g中的所有元素相加
asdfasdfasdfasdfasdf
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123
123123123123 asdfasdfasdfasdf
a.txt
程序四:
常规方法:
money_l=[]
with open('b.txt') as f:
for line in f:
goods=line.split()
res=float(goods[-1])*float(goods[-2])
money_l.append(res)
print(money_l)
---->[30.0, 1000000.0, 6000.0, 90000.0, 30.0]
生成器表达式写法:
f=open('b.txt')
g=(float(line.split()[-1])*float(line.split()[-2]) for line in f) print(sum(g))
---->1096060.0
程序五:
res=[]
with open('b.txt') as f:
for line in f:
# print(line)
l=line.split()
# print(l)
d={}
d['name']=l[0]
d['price']=l[1]
d['count']=l[2]
res.append(d) print(res)
---->[{'name': 'apple', 'price': '10', 'count': '3'}, {'name': 'tesla', 'price': '1000000', 'count': '1'}, {'name': 'mac', 'price': '3000', 'count': '2'}, {'name': 'lenovo', 'price': '30000', 'count': '3'}, {'name': 'chicken', 'price': '10', 'count': '3'}]
生成器表达式写法:
with open('b.txt') as f:
res=(line.split() for line in f)
print(res)
dic_g=({'name':i[0],'price':i[1],'count':i[2]} for i in res)
print(dic_g)
apple_dic=next(dic_g)
print(apple_dic['count']) apple_dict=next(dic_g)
print(apple_dict)
---->{'name': 'tesla', 'price': '1000000', 'count': '1'}
apple 10 3
tesla 1000000 1
mac 3000 2
lenovo 30000 3
chicken 10 3
b.txt
#取出单价>10000
with open('b.txt') as f:
res=(line.split() for line in f)
# print(res)
dic_g=({'name':i[0],'price':i[1],'count':i[2]} for i in res if float(i[1]) > 10000)
print(dic_g)
----> <generator object <genexpr> at 0x0000000001E05888>
print(list(dic_g))
----> [{'name': 'tesla', 'price': '1000000', 'count': '1'}, {'name': 'lenovo', 'price': '30000', 'count': '3'}]
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