Python notes--dictionaries

Dictionary dict

Dictionaries are stored using key-value (key-value) keys, which must be different from one another in a dictionary.

The dictionary has a very fast speed, because the use of key-value storage, when put in the key to calculate the vlaue location, so that key can be directly located to the value .

The sequence is indexed by successive integers, and unlike dictionaries, the dictionary is indexed by a keyword, which can be any immutable object (not modifiable), usually a string or numeric value, which also guarantees that the storage location of value does not change.

Since a key can only correspond to one value, the value is placed on a key more than once, and subsequent values flush out the previous value.

It takes a lot of memory, and it wastes a lot of memory.

First, Defining Dictionaries

>>> name={' Zhangsan ': All, ' Lisi ':, ' Wangwu ': 70}

With curly braces, keys and values are separated by colons, and multiple key-values are separated by commas, and a key can only correspond to one value.

Second, Basic Operations

#返回所有键值

>>> name.items (' Wangwu ', 70) [(' Lisi ', '), (' Zhangsan ', ' + ')]

#返回所有键

>>> Name.keys () [' Lisi ', ' Zhangsan ', ' Wangwu ']

#返回所有值

>>> name.values () [80, 90, 70]

Note: The results returned above are in the form of a list

#添加键值

>>> name[' Zhaoliu ']=60>>> name{' Lisi ': $, ' Zhaoliu ': $, ' Zhangsan ': $, ' Wangwu ': 70}

#获取单个键的值

>>> name[' Zhangsan ']90

Note: If this key does not exist, it will output keyerror error

>>> name.get (' Zhangsan ') 90

Note: If this key does not exist, the output is empty.

#删除指定指定的键值

>>> name.pop (' Zhangsan ') 90>>> name{' Lisi ': $, ' Zhaoliu ': $, ' Wangwu ': 70}

#删除第一个键值

>>> name.popitem (' Lisi ', +) >>> name{' Zhaoliu ': $, ' Wangwu ': 70}

#把其他字典的键值添加到本字典中

>>> name{' Zhaoliu ': $, ' Wangwu ': 70}>>> name1={' Jerry ': A, ' Mike ':66}>>> name.update ( name1) >>> name{' Mike ': 70, ' Zhaoliu ': $, ' Jerry ': "Wangwu

#拷贝为一个新的字典

>>> name2=name.copy () >>> name2{' Mike ': 70, ' Zhaoliu ': $, ' Jerry ': "Wangwu

Note: name2 does not change with name

>>> name3=name>>> name3{' Mike ': 70, ' Zhaoliu ': $, ' Jerry ':, ' Wangwu

Note: The Name3 will change with name

#判断字典中是否有这个键

>>> name.has_key (' Wangwu ') true>>> name.has_key (' FJC ') False

#如果字典中有这个键, the corresponding value is returned, not the key is added to the dictionary, the value defaults to None

>>> name{' Mike ': The ' Zhaoliu ': $, ' Jerry ': The ' Wangwu ': 70}>>> name.setdefault (' Mike ') 66>> > Name.setdefault (' Mike ', 66>>> Name.setdefault (' Mike '), 66>>> name{' Mike ': ' Zhaoliu ': ' Jerry ': ' Wangwu ': 70}>>> name.setdefault (' FJC ') >>> name{' Mike ': The ' FJC ': None, ' Zhaoliu ': 60 , ' Jerry ': ' Wangwu ': 70}>>> name.setdefault (' Miss ', ') ' 50>>> name{' Mike ': The ' FJC ': None, ' Zhaoliu ' ': ' Miss ': ' Jerry ': ' Wangwu ': 70}

Note: The parentheses in. SetDefault () can contain both the key and the value.

#根据一个列表生成字典中的键, the value is none

>>> lst=[1,2,3,4,5]>>> Dic={}.fromkeys (LST) >>> Dic{1:none, 2:none, 3:none, 4:none, 5:none}

#清空字典

>>> dic.clear () >>> dic{}

#字典迭代器

. Iteritems () # Get all key values

. Iterkeys () # Get all keys

. Itervalues () # Get all values

>>> a=name.iteritems () >>> a.next (' Mike ', 66)

Note: multiple executions. Next () to list key values

#一个键多个值

is to change the value to a list, a tuple, or a dictionary

>>> b={' a ': [2], ' B ':2}>>> c={' a ':(, ' B ':2}>>> d={' a ': {' C ': 3, ' d ': 4}, ' B ':}

This article is from the "Network Technology" blog, please be sure to keep this source http://fengjicheng.blog.51cto.com/11891287/1927625

Python notes--dictionaries