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Another variable is the dictionary container model, and can store any type of object.
Each dictionary key (key => value) of the colon(:) divided between each pair with a comma (,)division, including the entire dictionary in curly braces({}),the format is as follows:
d = {key1 : value1, key2 : value2 }
Key must be unique, but the value is not necessary.
Value can take any data type, but the key must be immutable, such as strings, numbers, or tuples.
A simple dictionary Example:
dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}
So also create the dictionary:
dict1 = { 'abc': 456 }; dict2 = { 'abc': 123, 98.6: 37 };
The corresponding key in the familiar square brackets following examples:
#!/usr/bin/python3 dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} print ("dict['Name']: ", dict['Name']) print ("dict['Age']: ", dict['Age'])
Examples of the above output:
dict['Name']: w3resource dict['Age']: 7
If there is no key to access the data dictionary, it will output the following error:
#!/usr/bin/python3 dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'}; print ("dict['Alice']: ", dict['Alice'])
Examples of the above output:
Traceback (most recent call last): File "test.py", line 5, in <module> print ("dict['Alice']: ", dict['Alice']) KeyError: 'Alice'
Way to add new content to the dictionary to add new key / value pairs, modify or delete existing key / value pairs following examples:
#!/usr/bin/python3 dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} dict['Age'] = 8; # 更新 Age dict['School'] = "本教程" # 添加信息 print ("dict['Age']: ", dict['Age']) print ("dict['School']: ", dict['School'])Examples of the above output:
dict['Age']: 8 dict['School']: 本教程
Can delete a single element can be empty dictionary, emptied just one operation.
To delete a dictionary with the del command, the following examples:
#!/usr/bin/python3 dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} del dict['Name'] # 删除键 'Name' dict.clear() # 删除字典 del dict # 删除字典 print ("dict['Age']: ", dict['Age']) print ("dict['School']: ", dict['School'])
But this raises an exception, because with the operation after performing del dictionaries no longer exists:
Traceback (most recent call last): File "test.py", line 9, in <module> print ("dict['Age']: ", dict['Age']) TypeError: 'type' object is not subscriptable
NOTE: The next del () method will be discussed.
Dictionary values can be taken without limitation, any python object can be both standard object, it can be user-defined, but the key does not work.
Two important points to remember:
1) does not allow the same key appears twice. When you create is assigned if the same key twice, the latter value will be remembered, the following examples:
#!/usr/bin/python3 dict = {'Name': 'w3resource', 'Age': 7, 'Name': '小本'} print ("dict['Name']: ", dict['Name'])
Examples of the above output:
dict['Name']: 小本
2) key must not be changed, so you can use numeric, string, or tuple to act as, and will not work with the list, the following examples:
#!/usr/bin/python3 dict = {['Name']: 'w3resource', 'Age': 7} print ("dict['Name']: ", dict['Name'])
Examples of the above output:
Traceback (most recent call last): File "test.py", line 3, in <module> dict = {['Name']: 'w3resource', 'Age': 7} TypeError: unhashable type: 'list'
Python dictionary contains the following built-in functions:
No. | Function and description | Examples |
---|---|---|
1 | len (dict) Counting the number of dictionary elements, namely the total number of keys. | >>> dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} >>> len(dict) 3 |
2 | str (dict) Output dictionaries printable string representation. | >>> dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} >>> str(dict) "{'Name': 'w3resource', 'Class': 'First', 'Age': 7}" |
3 | type (variable) Returns the type of input variable, if the variable is a dictionary returns a dictionary. | >>> dict = {'Name': 'w3resource', 'Age': 7, 'Class': 'First'} >>> type(dict) <class 'dict'> |
Python dictionary contains the following built-in method:
No. | Function and description |
---|---|
1 | radiansdict.clear () Delete all the elements in the dictionary |
2 | radiansdict.copy () Returns a shallow copy of dictionary |
3 | radiansdict.fromkeys () Create a new dictionary to the sequence seq elements do dictionary key, val as a dictionary of all the key corresponding to the initial value |
4 | radiansdict.get (key, default = None) Returns the value of the specified key, if the return value is not in the dictionary default values |
5 | key in dict Returns true if the key is in the dictionary dict, otherwise returns false |
6 | radiansdict.items () Returns a list traversal (key, value) tuples array |
7 | radiansdict.keys () To return a list of all the keys dictionary |
8 | radiansdict.setdefault (key, default = None) And get () is similar, but if the key does not exist in the dictionary, and will add value to default keys |
9 | radiansdict.update (dict2) Dict2 the dictionary of key / value pairs in the update to the dict |
10 | radiansdict.values () To return a list of all the values in the dictionary |