Python Basics 6 (dictionary)

Mappings : Relationship of key-value pairs, key (key) mapping values (value)

The dictionary is the only type of mapping for Python

>>> Phonebook = {'Wakey':'1111','Ethon':'2222','Joho':'3333'}>>>phonebook{'Joho':'3333','Wakey':'1111','Ethon':'2222'}

Extension: the difference between a mapping type and a sequence type

1, Access way, sequence type with a numeric type of key, and the mapping type can be used other object type key (General string)

>>> lis = ['a','b','C']>>> lis[2]'C'>>> dic = {'name':'a','Father':'b','Mother':'C'}>>> dic['Mother']'C'

2, the storage type is different, the mapping type key, directly or indirectly is related to the value.

3. Sequence type, ordered column; map type is unordered

Dictionary:

1. dict function

>>> items = [('name','Gumby'),(' Age', 42)]#Create a dictionary from other mappings or key-value pairs>>> d =dict (items)>>>d{' Age': 42,'name':'Gumby'}>>> >>> d = dict (name='Ethon', age=42)#creating a dictionary with keyword parameters>>>d{' Age': 42,'name':'Ethon'}

2. Dictionary Features:

1) The key can be any immutable type (the most powerful place in the dictionary)

2) keys in the dictionary may be added automatically

>>> x = {}     #  empty dictionary >>> x[2]='ethon'>>>  x{'ethon'}

3. Dictionary method

Dict.clear (): Delete all elements in the dictionary

>>> x = {'name':'wakey',' age ' ': >>> x.clear ()>>> x{}

Dict.copy (): Returns a new dictionary with the same key-value pair

>>> x = {'name':'Wakey',' Age': 22}>>> y =x.copy ()>>> y['name']='Ethon'>>>y{' Age': 22,'name':'Ethon'}>>>x{' Age': 22,'name':'Wakey'}

Dict.formkeys (): Create a new dictionary with the given key

>>> {}.fromkeys (['name','age']) {'  Age'name': none}    #  None as default

Dict.get (Key,default=none): Returns the corresponding key value

>>> d = {}print d.get ('name')     None        # get access to a nonexistent key when you get the None value

Dict.has_key (): Check if key exists

>>> d = {}>>> D.has_key ('name') False>>> d[ ' name '] ='ethon'>>> d.has_key ('name') True 

Dict.items (): Returns all dictionary entries as a list, with no specific order of items returned.

>>> d = {'title':'Python web site','URL':'http://www.python.com'}>>>D.items () [('URL','http://www.python.com'), ('title','Python web site')]

Dict.keys (): List of Keys dict.values (): List of values

Dict.pop (): Gets the value corresponding to the given key, and then removes the key-value pair from the dictionary

>>> d = {'x': 1,'y': 2}>>> D.pop ( ' x ' )1>>> d{'y': 2}

Dict.popitem (): The last element of the pop-up list (random popup), this method is useful if you want to remove and manipulate items one by one.

>>> d = {'title':'python','URL':'www.python,com'}>>>D.popitem () ('URL','www.python,com')>>>d{'title':'python'}

Dict.update (): Update another dictionary with one dictionary item

>>> d = {'title':'python','URL':'www.python,com'}>>> x = {'title':'Python language website'}>>>d.update (x)>>>d{'URL':'www.python,com','title':'Python language website'}

Python Basics 6 (dictionary)