原标题:Python知识点总结篇(二)
原文来自:博客园 原文链接:https://www.cnblogs.com/cunyu1943/p/11606062.html
列表
列表:一个值,包含多个字构成的序列,用[ ]
括起来,[]
是一个空列表,不包含任何值,类似于空字符串,负数下标表示从后边开始,-1
表示列表最后一个下标,它是一种可变的数据类型,值可以添加、删除或改变;
+
用于连接两个列表并得到一个新列表;*
用于一个列表和一个整数,实现列表的复制;del
将删除列表中下标处的值;in
、not in
用于确定一个值是否在列表中;
多重赋值技巧:变量数目和列表长度必须严格相等,eg;
cat = ['fat', 'black', 'loud']
size, color, disposition = cat
supplies = ['pens', 'staplers', 'flame-throwers', 'binders']
supplies.sort()
print(supplies)
supplies = ['pens', 'staplers', 'flame-throwers', 'binders']
sortedSupplies = sorted(supplies)
print(supplies)
print(sortedSupplies)
#序列转元组pets = ['K', 'M', 'N']
print(tuple(pets))#元组转序列pets = ('K', 'M', 'N')
print(list(pets))
>>> spam = [0, 1, 2, 4, 5]>>> chees = spam>>> cheese[1] = 'Hello'>>> spam
[0, 'Hello', 2, 4, 5]>>> cheese
[0, 'Hello', 2, 4, 5]
字典和结构化数据
字典:{key:value}
;
字典与列表:列表是有序的,而字典是无序的,因此字典不可像列表一样切片;
keys()
、values()
、items()
:分别对应于字典的键、值和键-值对;
get(要取得其值的键, 键不存在时返回的备用值)
:
>>> picnicItems = {'apples':5, 'cpus':2}>>> 'I am bringing ' + str(picnicItems.get('cups', 0) + ' cups.'I am bringing 2 cups.>>> 'I an bringing ' + str(picnicItems.get('eggs', 0) + ' cups.'I am bringing 0 eggs.
>>> spam = {'name':'Pooka', 'age':5}>>> spam.setdefault('color', 'black')'black'>>> spam
{'color':'black', 'age':5, 'name':'Pooka'}>>> spam.setdefault('color', 'white')'black'>>> spam
{'color':'black', 'age':5, 'name':'Pooka'}
集合:无序、不重复的数据组合,主要作用为:
格式输出:pprint()
和pformat()
;
import pprint
info = {'name':'K', 'age': 23}
pprint.pprint(info)#下列这句和上句结果相同#print(pprint.pformat(info))
#嵌套的字典和列表allGuests = {'Alice':{'apple':4, 'pretzels':19}, 'Bob':{'apple':3, 'sandwiches':4}, 'Carol':{'cups':5, 'apple pies':4}}def totalBrought(guests, item):
numberBrought = 0; for k, v in guests.items():
numberBrought += v.get(item, 0) return numberBrought
print('Apple = ' + str(totalBrought(allGuests, 'apple')))
字符串操作
>>> print(r'That is Carol's cat.')
That is Carol's cat.
>>> print('''Dear Alice,
Eve's cat has been arrested for catnapping, cat burglary, and extortion.
Sincerely,
Bob''')
Dear Alice,
Eve's cat has been arrested for catnapping, cat burglary, and extortion.
Sincerely,
Bob
免责声明:本文来自互联网新闻客户端自媒体,不代表本网的观点和立场。
合作及投稿邮箱:E-mail:editor@tusaishared.com