Each dictionary key key => value of the colon : split, between each key pair with a comma, segmentation , the whole dictionary includes in braces {} in the following format:
d = {key1 : value1, key2 : value2 }
Generally unique key, if the last repetition of a key-value replaces the preceding value need not be unique .
>>>dict = {'a': 1, 'b': 2, 'b': '3'}
>>> dict['b']
'3'
>>> dict
{'a': 1, 'b': '3'}Type of data may take any value
A simple example dictionary:
dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}
So also create a dictionary:
dict1 = { 'abc': 456 } dict2 = { 'abc': 123, 98.6: 37 }
Access the dictionary values
The corresponding key in square brackets , the following examples:
Examples
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print "dict['Name']: ", dict['Name']
print "dict['Age']: ", dict['Age']Examples of the above output:
dict['Name']: Zara dict['Age']: 7
If there are no keys to access the data dictionary, it will output an error KeyError
Modifying a dictionary
Way to add new content to the dictionary to add new key / value pairs, modify, or delete existing key / value pairs in the following examples:
Examples
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
dict['Age'] = 8 # 更新
dict['School'] = "RUNOOB" # 添加
print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']Examples of the above output:
dict['Age']: 8 dict['School']: RUNOOB
Delete dictionary elements
Can delete a single element can be empty dictionary , emptied just one operation.
Delete a dictionary with the del command, the following examples:
Examples
#!/usr/bin/python
# -*- coding: UTF-8 -*-
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
del dict['Name'] # 删除键是'Name'的条目
dict.clear() # 清空字典所有条目
del dict # 删除字典
print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']But this raises an exception, because there is no longer with the del dictionaries:
dict['Age']:
Traceback (most recent call last):
File "test.py", line 8, in <module>
print "dict['Age']: ", dict['Age']
TypeError: 'type' object is unsubscriptable
Key characteristics of the dictionary
There is no limit value may be , a standard or user-defined objects , but not the key.
Two important points to remember:
1) does not allow the same key appears twice. When you create If the assigned the same key twice, the last value will be remembered , the following examples:
Examples
#!/usr/bin/python
dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'}
print "dict['Name']: ", dict['Name']Examples of the above output:
dict['Name']: Manni
2) key must not be changed, it can be numbers, strings, or act as a tuple, it will not work with the list, the following examples:
Examples
#!/usr/bin/python
dict = {['Name']: 'Zara', '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']: 'Zara', 'Age': 7}
TypeError: list objects are unhashable
Dictionary built-in functions & methods
Function: The Name of the class to call;
Methods: Object xxx.xx () to call;
Python dictionary contains the following built-in functions:
| No. | Functions and Description |
|---|---|
| 1 | cmp (dict1, dict2) to compare two elements in the dictionary. |
| 2 | len (dict) calculated total number of dictionary elements, i.e. bond. |
| 3 | str (dict) string dictionary printable output representation. |
| 4 | type (variable) returns the type of input variables, if the variable is a dictionary returns a dictionary. |
Python dictionary contains the following built-in method:
| No. | Functions and Description |
|---|---|
| 1 | dict.clear () All elements in the deleted dictionary |
| 2 | dict.copy () Returns a shallow copy of the dictionary |
| 3 | dict.fromkeys (seq [, val]) creates a new dictionary, the sequence elements do seq dictionary key, val a dictionary initial value corresponding to all keys |
| 4 | dict.get (key, default = None) Returns the specified key, if the return value is not in the dictionary default value |
| 5 | dict.has_key (key) if the key is in the dictionary dict returns true, otherwise returns false |
| 6 | dict.items () to return may traverse the list (key, value) tuples array |
| 7 | dict.keys () to return a list of all the keys dictionary |
| 8 | dict.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 | dict.update (dict2) to dict2 dictionary of key / value pairs in the update to the dict |
| 10 | dict.values () all values in the list returned dictionary |
| 11 | pop (key [, default]) value of a given key to delete the dictionary corresponding to the key, the return value is deleted. key value must be given. Otherwise, return default values. |
| 12 | popitem () to go back and delete the last pair of keys and values in the dictionary. |
