python之dictionary

dict1 = {key1:value1,key2:value2}

>>> dict1 = {‘name‘:‘python‘,‘age‘:‘20‘,‘character‘:‘scripts‘}

>>> dict1 = {‘name‘:‘python‘,‘age‘:‘20‘,‘character‘:‘scripts‘}
>>> print(dict1[‘name‘])
python
>>> print(dict1[‘age‘])
20
>>> print(dict1[‘age1‘])
Traceback (most recent call last):
  File "", line 1, in
KeyError: ‘age1

>>> dict2 = {‘key1‘:123,‘key2‘:‘dictionary‘}
>>> dict2[‘key1‘]=888 #修改对应的key的值
>>> print(dict2)
{‘key2‘: ‘dictionary‘, ‘key1‘: 888}
>>> dict2[‘key3‘]=‘python3‘ #给字典添加元素
>>> print(dict2)
{‘key2‘: ‘dictionary‘, ‘key1‘: 888, ‘key3‘: ‘python3‘}
>>> del dict2[‘key1‘] #删除键
>>> print(dict2)
{‘key2‘: ‘dictionary‘, ‘key3‘: ‘python3‘}
>>> dict2.clear() #清空字典内容
>>> dict2
{}
>>> del dict2 #删除字典
>>> dict2
Traceback (most recent call last):
File "", line 1, in
NameError: name ‘dict2‘ is not defined
#字典值可以没有限制地取任何python对象，既可以是标准的对象，也可以是用户定义的，但键不行。
#不允许同一个键出现两次。创建时如果同一个键被赋值两次，后一个值会被记住
>>> dict = {1:‘a‘,2:‘b‘,1:‘c‘}
>>> print(dict)
{1: ‘c‘, 2: ‘b‘}
#键必须不可变，所以可以用数字，字符串或元组充当，而用列表就不行
>>> dict = {1:‘a‘,‘abc‘:‘python‘,(‘tuple‘,‘values‘):‘abc‘,[‘list1‘]:‘listname‘}
Traceback (most recent call last):
File "", line 1, in
TypeError: unhashable type: ‘list‘

>>> dict1 = {1:‘a‘,2:‘b‘,3:‘c‘,4:‘d‘}
>>> len(dict1) #计算字段元素个数
4
>>> str(dict1) #输出字典，以可以打印的字符串表示
"{1: ‘a‘, 2: ‘b‘, 3: ‘c‘, 4: ‘d‘}"
>>> type(dict1) #返回变量类型
<class ‘dict‘>

>>> dict = {‘a‘:1,‘b‘:2}
>>> dict.clear() #清除字典内的所有元素
>>> dict
{}
>>> dict = {‘a‘:1,‘b‘:{‘c‘:22,‘d‘:33}}
>>> dict1 = dict.copy() #返回字典的浅复制，即只拷贝第一层键对应值
>>> dict1
{‘b‘: {‘d‘: 33, ‘c‘: 22}, ‘a‘: 1}
>>> dict1.fromkeys(range(5),‘000‘) #创建一个新字典，迭代序列做字典的键，value为字典的初始值，此处为"000"
{0: ‘000‘, 1: ‘000‘, 2: ‘000‘, 3: ‘000‘, 4: ‘000‘}
>>> dict1 = {‘k1‘:‘v1‘,‘k2‘:‘v2‘}
>>> print(dict1.get(‘k3‘)) #get查找key是否存在，如果不存在则用None，或指定值
None
>>> print(dict1.get(‘k3‘,‘python‘))
python
>>> ‘k1‘ in dict1 #判断键是否存在，存在返回true，否则返回false
True
>>> ‘k3‘ in dict1
False
>>> dic = {‘k1‘:‘v1‘,‘k2‘:‘v2‘}
>>> print(dic.items()) #以列表返回可遍历的(键, 值) 元组数组
dict_items([(‘k1‘, ‘v1‘), (‘k2‘, ‘v2‘)])

>>> print(dic.keys()) #以列表返回字典的所有键
dict_keys([‘k1‘, ‘k2‘])
>>> print(dic.values()) #以列表返回字典的所有值
dict_values([‘v1‘, ‘v2‘])
>>> dic.setdefault(‘k3‘,‘v3‘) #和get()类似, 但如果键不存在于字典中，将会添加键并将值设为default或指定
‘v3‘
>>> dic
{‘k1‘: ‘v1‘, ‘k3‘: ‘v3‘, ‘k2‘: ‘v2‘}
>>> dic1 = {1:22,2:33,3:44}
>>> dic.update(dic1) #把字典dic1的键/值对更新到dic里
>>> dic
{1: 22, 2: 33, 3: 44, ‘k3‘: ‘v3‘, ‘k1‘: ‘v1‘, ‘k2‘: ‘v2‘}
>>> dic.pop(1) #删除字典给定的键值，返回值为删除的值，key必须指定，如删除键不存在则返回default值，可指定。
22
>>> dic
{2: 33, 3: 44, ‘k3‘: ‘v3‘, ‘k1‘: ‘v1‘, ‘k2‘: ‘v2‘}
>>> dic.pop(1,‘hehe‘)
‘hehe‘
>>> dic.popitem() #随机删除字典中的一对键和值(一般删除最前的对)
(2, 33)
>>> dic.popitem()
(3, 44)

根据奇数和偶数生成字典元素
dct1 = {}
for i in range(20):
if i%2 == 1:
if ‘odd‘ in dct1.keys():
dct1[‘odd‘].append(i)
else:
dct1[‘odd‘] = [i,]
else:
if ‘even‘ in dct1.keys():
dct1[‘even‘].append(i)
else:
dct1[‘even‘] = [i,]
print(dct1)
输出结果：
{‘odd‘: [1, 3, 5, 7, 9, 11, 13, 15, 17, 19], ‘even‘: [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]}
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