Python Dictionary
The dictionary is another variable container model and can store any type of object.
Each key value for the dictionary key=>value is split with a colon :, each key-value pair Intersected with a comma ,, the entire dictionary is enclosed in curly braces {} in the following format:
d = {key1 : value1, key2 : value2 }
The
key is generally unique. If the last key-value pair is repeated, the value does not need to be unique.
>>>dict = {'a': 1, 'b': 2, 'b': '3'}
>>> dict[ 'b']
'3'< Span class="hl-code">
>>> dict
{'a' : 1, 'b' : '3' }
The
value can take any data type, but the keys must be immutable, such as strings, numbers, or tuples.
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 }
Access the value in the dictionary
Put the corresponding key into the familiar square bracket, as in the following example:
Instance
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print "dict['Name']: ", dict['Name']
print "dict['Age']: ", dict['Age']
The above example output：
dict['Name']: Zara
dict['Age']: 7
If you access the data with a key that is not in the dictionary, the error will be output as follows：
Instance
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print "dict['Alice']: ", dict['Alice']
The above example output：
dict['Alice']:
Traceback (most recent call last):
File "test.py", line 5, in <module>
print "dict['Alice']: ", dict['Alice']
KeyError: 'Alice'
Modify dictionary
Adding new content to the dictionary is by adding new key/value pairs, modifying or deleting existing key/value pairs as follows:
Instance
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
dict['Age'] = 8
dict['School'] = "RUNOOB"
print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']
The above example output：
dict['Age']: 8
dict['School']: RUNOOB
Delete dictionary elements
The ability to delete a single element can also clear the dictionary, emptying only one operation.
Show delete a dictionary with the del command, as in the following example:
Instance
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
del dict['Name']
dict.clear()
del dict
print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']
But this will cause an exception, because the dictionary no longer exists after using del：
dict['Age']:
Traceback (most recent call last):
File "test.py", line 8, in <module>
print "dict['Age']: ", dict['Age']
TypeError: 'type' object is unsubscriptable
Note：del()The method will also be discussed later.。
Characteristics of dictionary keys
The dictionary value can take any python object without restriction, either as a standard object or as a user-defined one, but not a key.
Two important points to remember:
1) The same key is not allowed to appear twice. If the same key is assigned twice when creating, the latter value will be remembered, as in the following example:
Instance
dict = {' Name': 'Zara' , 'Age' : 7, 'Name' : 'Manni' }
print "dict['Name']: ", < Span class="hl-identifier">dict['Name']
The output of the above example:
dict['Name' ]: Manni
2) The key must be immutable, so it can be played with numbers, strings or tuples, so using the list will not work, as in the following example:
Instance
dict = {[ 'Name']: ' Zara', ' Age': 7}
print "dict['Name']: ", < Span class="hl-identifier">dict['Name']
The above example output：
Traceback (most recent call last):
File "test.py", line 3, in <module>
dict = {['Name']: 'Zara', 'Age': 7}
TypeError: list objects are unhashable