Python中dict详解

from：http://www.cnblogs.com/yangyongzhi/archive/2012/09/17/2688326.html

Python中dict详解

python3.0以上，print函数应为print（），不存在dict.iteritems()这个函数。

在python中写中文注释会报错，这时只要在头部加上# coding=gbk即可

#字典的添加、删除、修改操作
dict = {"a" : "apple", "b" : "banana", "g" : "grape", "o" : "orange"}
dict["w"] = "watermelon"
del(dict["a"])
dict["g"] = "grapefruit"
print dict.pop("b")
print dict
dict.clear()
print dict
#字典的遍历
dict = {"a" : "apple", "b" : "banana", "g" : "grape", "o" : "orange"}
for k in dict:
    print "dict[%s] =" % k,dict[k]
#字典items()的使用
dict = {"a" : "apple", "b" : "banana", "c" : "grape", "d" : "orange"}
#每个元素是一个key和value组成的元组，以列表的方式输出
print dict.items()
#调用items()实现字典的遍历
dict = {"a" : "apple", "b" : "banana", "g" : "grape", "o" : "orange"}
for (k, v) in dict.items():
    print "dict[%s] =" % k, v
#调用iteritems()实现字典的遍历
dict = {"a" : "apple", "b" : "banana", "c" : "grape", "d" : "orange"}
print dict.iteritems()
for k, v in dict.iteritems():
    print "dict[%s] =" % k, v
for (k, v) in zip(dict.iterkeys(), dict.itervalues()):
    print "dict[%s] =" % k, v
   
#使用列表、字典作为字典的值
dict = {"a" : ("apple",), "bo" : {"b" : "banana", "o" : "orange"}, "g" : ["grape","grapefruit"]}
print dict["a"]
print dict["a"][0]
print dict["bo"]
print dict["bo"]["o"]
print dict["g"]
print dict["g"][1]
 
dict = {"a" : "apple", "b" : "banana", "c" : "grape", "d" : "orange"}
#输出key的列表
print dict.keys()
#输出value的列表
print dict.values()
#每个元素是一个key和value组成的元组，以列表的方式输出
print dict.items()
dict = {"a" : "apple", "b" : "banana", "c" : "grape", "d" : "orange"}
it = dict.iteritems()
print it
#字典中元素的获取方法
dict = {"a" : "apple", "b" : "banana", "c" : "grape", "d" : "orange"}
print dict
print dict.get("c", "apple")         
print dict.get("e", "apple")
#get()的等价语句
D = {"key1" : "value1", "key2" : "value2"}
if "key1" in D:
    print D["key1"]
else:
    print "None"
#字典的更新
dict = {"a" : "apple", "b" : "banana"}
print dict
dict2 = {"c" : "grape", "d" : "orange"}
dict.update(dict2)
print dict
#udpate()的等价语句
D = {"key1" : "value1", "key2" : "value2"}
E = {"key3" : "value3", "key4" : "value4"}
for k in E:
    D[k] = E[k]
print D
#字典E中含有字典D中的key
D = {"key1" : "value1", "key2" : "value2"}
E = {"key2" : "value3", "key4" : "value4"}
for k in E:
    D[k] = E[k]
print D
#设置默认值
dict = {}
dict.setdefault("a")
print dict
dict["a"] = "apple"
dict.setdefault("a","default")
print dict
#调用sorted()排序
dict = {"a" : "apple", "b" : "grape", "c" : "orange", "d" : "banana"}
print dict  
#按照key排序 
print sorted(dict.items(), key=lambda d: d[0])
#按照value排序 
print sorted(dict.items(), key=lambda d: d[1])
#字典的浅拷贝
dict = {"a" : "apple", "b" : "grape"}
dict2 = {"c" : "orange", "d" : "banana"}
dict2 = dict.copy()
print dict2

#字典的深拷贝
import copy
dict = {"a" : "apple", "b" : {"g" : "grape","o" : "orange"}}
dict2 = copy.deepcopy(dict)
dict3 = copy.copy(dict)
dict2["b"]["g"] = "orange"
print dict
dict3["b"]["g"] = "orange"
print dict

补充：
1 初始化
>>> d = dict(name='visaya', age=20)
>>> d = dict(zip(['name', 'age'], ['visaya', 20]))

#dict.fromkeys(listkeys, default=0) 把listkeys中的元素作为key均赋值为value，默认为0
>>> d = dict.fromkeys(['a', 'b'], 1)
>>> d
{'a': 1, 'b': 1}
2 字典视图和几何
dict.keys()类似信使可以进行交集和并集等集合操作（类似集合，因为不存在重复的项），但dict.values()不可以进行如上操作。

>>> k = d.keys()
>>> k
dict_keys(['a', 'b'])
>>> list(k)
['a', 'b']
>>> k | {'x': 3}
{'a', 'x', 'b'}
>>> k | {'x'}
{'a', 'x', 'b'}
>>> k | {'x', 'y'}
{'a', 'y', 'b', 'x'}
>>> k & {'x'}
set()
>>> v = d.values()
>>> v
dict_values([1, 2])
>>> v | {'x'}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for |: 'dict_values' and 'set'
3 排序字典键
两种方法:
3.1 sort:
>>> Ks = list(d.keys())
>>> Ks.sort()
>>> for k in Ks:
...     print(k, d[k])
... 
a 1
b 2
3.2 sorted:
>>> for k in sorted(d.keys()):
...     print(k, d[k])
... 
a 1
b 2

3.3 注意
>>> for k in list(d.keys()).sort():
...     print(k, d[k])
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not iterable

出错原因：
list.sort() list.append()函数都是对自身的操作，没有返回值，故需先将list(d.keys())的结果保存下来，在结果上进行sort()
4 常用函数
4.1 get()
D.get(k[, d])   => D[k] if k in D else d. d defaults to none.
4.2 pop()
D.pop(value[, d])   => Remove specified key and return the corresponding value. If key is not found, d is returned if given, otherwise KeyError is raised.
4.3 udpate()
    D.update(E, **F) -> None.  Update D from dict/iterable E and F.
    If E has a .keys() method, does:     for k in E: D[k] = E[k]
    If E lacks .keys() method, does:     for (k, v) in E: D[k] = v
    In either case, this is followed by: for k in F: D[k] = F[k]

>>> d = dict(name='visaya', age=21)
>>> d1= {'age': 20, 'sex': 'male'}
>>> d2 = zip(['a', 'b'], [1, 2])

>>> d.update(d1)
>>> d
{'age': 20, 'name': 'visaya', 'sex': 'male'}
#for k in d1: d[k] = d1[k]

>>> d.update(d2)
>>> d
{'age': 20, 'name': 'visaya', 'sex': 'male'}
#for (k, v) in d2: d[k] = v
4.4 del()
del D[key]
4.5 clear()
4.6 copy()
Python中的dict
初始化
构造方法创建
Python代码  
d = dict()  
d = dict(name="nico", age=23)  
d = dict((['name', "nico"], ['age', 23]))  
 当然还有更方便，简单的
Python代码  
d = {}  
d = {"name":"nico", "age":23}  
 
 
遍历
通过对key的遍历，遍历整个dict
 
Python代码  
d = {"name":"nico", "age":23}  
for key in d:  
    print "key=%s, value=%s" % (key, d[key])  
      
for key in d.iterkeys():  
    print "key=%s, value=%s" % (key, d[key])  
      
for key in d.keys():  
    print "key=%s, value=%s" % (key, d[key])  
      
for key in iter(d):  
    print "key=%s, value=%s" % (key, d[key])  
      
for key,item in d.items():  
    print "key=%s, value=%s" % (key, item)  
 
 当然也可以直接遍历value
 
Python代码  
d = {"name":"nico", "age":23}  
for value in d.values():  
    print value  
      
for key,value in d.viewitems():  
    print "key=%s, value=%s" % (key, value)  
  
for value in d.viewvalues():  
    print "value=%s" % (value)  
这里values和viewvalues的区别
 
后者返回的是该字典的一个view对象，类似数据库中的view，当dict改变时，该view对象也跟着改变
 
常用方法
 
Python代码  
d = {"name":"nico", "age":23}  
d["name"] = "aaaa"  
d["address"] = "abcdefg...."  
print d   #{'age': 23, 'name': 'aaaa', 'address': 'abcdefg....'}  
 
 
获取dict值
Python代码  
print d["name"]               #nico  
print d.get("name")         #nico  
 
 如果key不在dict中，返回default，没有为None
Python代码  
print d.get("namex", "aaa")       #aaa  
print d.get("namex")                  #None  
 
排序sorted()
Python代码  
d = {"name":"nico", "age":23}  
for key in sorted(d):  
    print "key=%s, value=%s" % (key, d[key])  
#key=age, value=23  
#key=name, value=nico  
 
 
删除del
Python代码  
d = {"name":"nico", "age":23}  
Python代码  
del d["name"]  
#如果key不在dict中，抛出KeyError  
del d["names"]  
Python代码  
Traceback (most recent call last):  
  File "F:\workspace\project\pydev\src\ddd\ddddd.py", line 64, in <module>  
    del d["names"]  
KeyError: 'names'  
 
 
清空clear()
Python代码  
d = {"name":"nico", "age":23}  
d.clear()  
print d                                                    #{}  
 
copy()
Python代码  
d1 = d.copy()               #{'age': 23, 'name': 'nico'}  
#使用返回view对象  
d2 = d1.viewitems()    #dict_items([('age', 23), ('name', 'nico')])  
#修改字典d1，新增元素  
d1["cc"] = "aaaaaa"   
print d2                   
#dict_items([('cc', 'aaaaaa'), ('age', 23), ('name', 'nico')])  
 
 
pop(key[, default])
如果key在dict中，返回，不在返回default
Python代码  
#如果key在dict中，返回，不在返回default  
print d.pop("name", "niccco")                #nico  
print d.pop("namezzz", "niccco")           #niccco  
#key不在dict中，且default值也没有，抛出KeyError  
print d.pop("namezzz")                         #此处抛出KeyError  
 
popitem()
删除并返回dict中任意的一个(key,value)队，如果字典为空会抛出KeyError
Python代码  
d = {"name":"nico", "age":23}  
print d.popitem()       #('age', 23)  
print d.popitem()       #('name', 'nico')  
#此时字典d已为空  
print d.popitem()      #此处会抛出KeyError  
 
update([other])
将字典other中的元素加到dict中，key重复时将用other中的值覆盖
Python代码  
d = {"name":"nico", "age":23}  
d2 = {"name":"jack", "abcd":123}  
d.update(d2)  
print d     #{'abcd': 123, 'age': 23, 'name': 'jack'}