May 10, 2021 Python2
A dictionary is another variable container model and can store any type of object.
Each key value of the dictionary is split with a colon (:), and between each pair is split with a comma (,), and the entire dictionary is included in the parenthesis (') in the following format:
d = {key1 : value1, key2 : value2 }The key must be unique, but the value does not have to be.
Values can take any data type, but keys must be immeascondable, such as strings, numbers, or yuans.
A simple dictionary example:
dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}You can also create a dictionary like this:
dict1 = { 'abc': 456 };
dict2 = { 'abc': 123, 98.6: 37 };Put the appropriate keys into familiar square brackets, as follows:
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print "dict['Name']: ", dict['Name'];
print "dict['Age']: ", dict['Age'];The above example output results:
dict['Name']: Zara
dict['Age']: 7If you access data with keys that are not in the dictionary, the output error is as follows:
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print "dict['Alice']: ", dict['Alice'];The above example output results:
dict['Zara']:
Traceback (most recent call last):
File "test.py", line 4, in <module>
print "dict['Alice']: ", dict['Alice'];
KeyError: 'Alice'The way to add new content to the dictionary is to add a new key/value pair and modify or delete an existing key/value pair as follows:
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School"; # Add new entry
print "dict['Age']: ", dict['Age'];
print "dict['School']: ", dict['School'];The above example output results:
dict['Age']: 8
dict['School']: DPS SchoolCan delete a single element can also empty the dictionary, emptying only one operation.
The display removes a dictionary with the del command, as follows:
#coding=utf-8
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
del dict['Name']; # 删除键是'Name'的条目
dict.clear(); # 清空词典所有条目
del dict ; # 删除词典
print "dict['Age']: ", dict['Age'];
print "dict['School']: ", dict['School'];However, this throws an exception because the dictionary no longer exists after del:
dict['Age']:
Traceback (most recent call last):
File "test.py", line 8, in <module>
print "dict['Age']: ", dict['Age'];
TypeError: 'type' object is unsubscriptableNote: The del() method is also discussed later.
The characteristics of the dictionary key
Dictionary values can take any Python object without restriction, neither a standard object nor a user-defined object, but the key does not.
There are two important points to keep in mind:
1) The same key is not allowed to appear twice. If the same key is assigned twice when it is created, the last value is remembered, as in the following example:
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'};
print "dict['Name']: ", dict['Name'];The above example output results:
dict['Name']: Manni2) The key must be imm changed, so you can use numbers, strings, or metagroups, so you can't use lists, as in the following examples:
#!/usr/bin/python
dict = {['Name']: 'Zara', 'Age': 7};
print "dict['Name']: ", dict['Name'];The above example output results:
Traceback (most recent call last):
File "test.py", line 3, in <module>
dict = {['Name']: 'Zara', 'Age': 7};
TypeError: list objects are unhashableThe Python dictionary contains the following built-in functions:
| Serial number | Functions and descriptions |
|---|---|
| 1 |
cmp(dict1, dict2)
Compare two dictionary elements. |
| 2 |
len(dict)
Calculates the number of dictionary elements, which is the total number of keys. |
| 3 |
str(dict)
The output dictionary can print a string represented. |
| 4 |
type(variable)
Returns the type of variable entered, and returns the dictionary type if the variable is a dictionary. |
The Python dictionary contains the following built-in functions:
| Serial number | Functions and descriptions |
|---|---|
| 1 |
radiansdict.clear()
Delete all elements in the dictionary |
| 2 |
radiansdict.copy()
Returns a shallow copy of a dictionary |
| 3 |
radiansdict.fromkeys()
Create a new dictionary with the elements in the sequence seq as the keys to the dictionary, and val is the initial value for all keys in the dictionary |
| 4 |
radiansdict.get(key, default=None)
Returns the value of the specified key, if the value does not return the default value in the dictionary |
| 5 |
radiansdict.has_key(key)
If the key returns True in the dictionary dict, otherwise false is returned |
| 6 |
radiansdict.items()
Returns an array of traversable (key, value) yuans in a list |
| 7 |
radiansdict.keys()
Returns all the keys of a dictionary in a list |
| 8 |
radiansdict.setdefault(key, default=None)
Similar to get(), but if the key does not already exist in the dictionary, the key is added and the value is set to default |
| 9 |
radiansdict.update(dict2)
Update the key/value pair of the dictionary dict2 to the dict |
| 10 |
radiansdict.values()
Returns all values in the dictionary in a list |
Instance:
Use Python to write a dictionary program:
The code is as follows:
#coding:utf-8
# 字典创建 while开关 字典添加 字典寻找
dictionary = {}
flag = 'a'
pape = 'a'
off = 'a'
while flag == 'a' or 'c' :
flag = raw_input("添加或查找单词 ?(a/c)")
if flag == "a" : # 开启
word = raw_input("输入单词(key):")
defintion = raw_input("输入定义值(value):")
dictionary[str(word)] = str(defintion) # 添加字典
print "添加成功!"
pape = raw_input("您是否要查找字典?(a/0)") #read
if pape == 'a':
print dictionary
else :
continue
elif flag == 'c':
check_word = raw_input("要查找的单词:") # 检索
for key in sorted(dictionary.keys()): # yes
if str(check_word) == key:
print "该单词存在! " ,key, dictionary[key]
break
else: # no
off = 'b'
if off == 'b':
print "抱歉，该值不存在！"
else: # 停止
print "error type"
breakThe test results are as follows:
添加或查找单词 ?(a/c)a
输入单词(key):w3c
输入定义值(value):w3cschool.cn
添加成功!
您是否要查找字典?(a/0)0
添加或查找单词 ?(a/c)c
要查找的单词:w3c
该单词存在! w3c w3cschool.cn
添加或查找单词 ?(a/c)