Python基础(十二) 字典的使用

Python基础(十二)  字典的使用

字典的初始化和基本操作

初始化:

phoneBook = {"Alice":"0458","Lily":"2548","Tom":"1786"}
#用dict函数初始化
phoneBook = dict(Alice = "0458",Lily = '2548')

#用dict函数和 (键,值) 初始化
items = [('Alice', '0458'),('Lily','2548')]
phoneBook = dict(items)

基本操作:

#根据键查找相应值
print phoneBook['Lily']
#输出键值对的个数
print len(phoneBook)
#修改某个键对应的值
phoneBook['Lily'] = '2579'
print phoneBook['Lily']
#删除某个键值
del phoneBook['Lily']
print phoneBook
print "Lily in phoneBook ? ","Lily" in phoneBook

字典常用函数

clear()

#clear()方法 清空字典中的所有项
dict_x = {}
dict_x['name'] = "value"
dict_y = dict_x
dict_x = {}
print "dict_x :",dict_x
print "dict_y :",dict_y

dict_x['name'] = "value"
dict_y = dict_x
dict_x.clear()
print "dict_x :",dict_x
print "dict_y :",dict_y

copy()

#copy() 方法 (浅拷贝)
dict_x = {"name":"Lily","phoneNum":"2579","friends":["Lucy","Lilei"]}
#字典y是x的一个浅拷贝
dict_y = dict_x.copy()
#替换字典y 的 name值 原字典x的name值不会跟着改变
dict_y["name"] = "LilyChange"
print r"dict_x[name] = ",dict_x["name"]
print r"dict_y[name] = ",dict_y["name"]
#修改字典y 的 friends值 原字典x的friends值会跟着改变
dict_y["friends"].remove("Lucy")
print r"dict_x[friends] = ",dict_x["friends"]
print r"dict_y[friends] = ",dict_y["friends"]

deepcopy(dict)

#deepcopy(dict) 方法 (深拷贝)
from copy import deepcopy
dict_x = {"name":"Lily","phoneNum":"2579","friends":["Lucy","Lilei"]}
#字典y是x的一个浅拷贝
dict_y = deepcopy(dict_x)
#替换字典y 的 name值 原字典x的name值不会跟着改变
dict_y["name"] = "LilyChange"
print r"dict_x[name] = ",dict_x["name"]
print r"dict_y[name] = ",dict_y["name"]
#修改字典y 的 friends值 原字典x的friends值不会跟着改变
dict_y["friends"].remove("Lucy")
print r"dict_x[friends] = ",dict_x["friends"]
print r"dict_y[friends] = ",dict_y["friends"]

fromkeys(['key1','key2'])

#fromkeys(['key1','key2'])使用给定键建立新的字典 每个键值的默认值为None
fromkeysdict = dict.fromkeys(['key1','key2'])
print fromkeysdict

get('key')

#get('key') 方法如果key不在字典中 则返回None 而 dictname['key']如果没有对应key在字典中则会报错
getDic = {}
#getDic["keyname"]  #此句会报错
print getDic.get("keyname")

has_key('key')

#has_key('key') 检查字典中是否拥有某个key
hasKeyDict = {"name":"Lily","age":12}
print hasKeyDict.has_key("name")
print hasKeyDict.has_key("grade")

items 和 iteritems

#items 方法将所有的字典项以列表的方式返回.这些列表项中的每一项都来自于(键,值)
#但是项在返回时没有固定顺序
mDict = {"title":"MyDict","Context":"this is my Dict for Test ","Author":"Guodong"}
myDictList = mDict.items()
print myDictList[1]

keys 和 iterkeys

#keys 和 iterkeys
#keys方法返回所有键的列表
#iterkeys方法返回键的迭代器
mDict = {"title":"MyDict","Context":"this is my Dict for keys ","Author":"Guodong"}
print mDict.keys()

pop('key')

#pop方法移除对应键的键值对
mDict = {"title":"MyDict","Context":"this is my Dict for keys ","Author":"Guodong"}
mDict.pop("title")
print mDict

popitem()

#popitem 随机弹出列表的某一项 (一般会弹出第一项 但是Python不确定一定总是第一项)
mDict = {"title":"MyDict","Context":"this is my Dict for keys ","Author":"Guodong"}
mDict.popitem()
print mDict

setdefault('key','value')

#setdefault 给键值设定一个初始值 

d = {}
#如果键不存在  会相应更新字典
d.setdefault('name',"none") 
print d
d['name'] = "Lily"
#如果键值已经存在 则不会改变原有值
d.setdefault('name',"none") 
print d

update(dict)

#update 通过另一个字典更新字典
d1 = {"name":"none","age":13}
d2 = {"name":"guodong"}
d1.update(d2)
print d1