How IOS developers learn Python Programming 8 - set type 3

This is my participation 11 Yue Gengwen challenges 8 God , Check out the activity details ：2021 The last time Gengwen challenge .

Bytes

stay Python3 in the future , String and bytes The types are completely separated ：

• character string In order to character Is processed in units .
• bytes The type is based on byte For units of .

bytes Data types are basically the same as string data types in all operations and uses, even in built-in methods , It is also an immutable sequence object .

call bytes() Generate bytes example . For the same string, if different encoding methods are used to generate bytes object , And you get different values ：

>>> a = b'hello'
>>> type(a)
<class 'bytes'>
>>> b = bytes('hello',encoding='utf8')
>>> type(b)
<class 'bytes'>
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bytes Type common conversion

• Byte to string

>>> d = b'world'
>>> d.decode()
'world'
>>> type(d)
<class 'bytes'>
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• String to byte

>>> e = 'world'
>>> e.encode()
b'world'
>>> type(e)
<class 'str'>
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aggregate set

set aggregate ： An unordered collection of non repeating elements , Basic functions include ：

• Relationship testing
• Eliminate duplicate elements

set Use braces {} Framing elements , And separated by commas ： ️ Be careful ： If you want to create an empty collection , Must use  set()  instead of  {} , Because the latter creates an empty dictionary .

>>> s = {1,2,3}
>>> s
{1, 2, 3}
>>> type(s)
<class 'set'>

>>> s = {}      #  Be careful , Empty {} Will default to dictionary 
>>> type(s)
<class 'dict'>
>>> s = set()                   #  Create an empty set ->new empty set object( Create an empty set )
>>> s
set()
>>> type(s)
<class 'set'>

>>> s = set([1,2,3,1,2,3,4])    #  Create set , duplicate removal 
>>> s
{1, 2, 3, 4}
>>> s1 = set("hello world")     #  Create set , duplicate removal 
>>> s1
{'h', 'd', 'o', ' ', 'e', 'l', 'r', 'w'}
>>> s2 = set(123)               #  Be careful , Need to pass in iteratable objects , and int Type of 123 Not at all , So wrong reporting 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
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Set add elements

adopt add(key) Method to add elements to set in , Can be added repeatedly , But it won't work ：

>>> s = set([1,2,3,1,2,3,4])
>>> s
{1, 2, 3, 4}
>>> s.add(3)            #  Add repeatedly , Automatic weight removal 
>>> s
{1, 2, 3, 4}
>>> s.add(6)            #  Add success 
>>> s
{1, 2, 3, 4, 6}
>>> s.add("cat")        #  Add success 
>>> s
{1, 2, 3, 4, 6, 'cat'}
>>> s.add([1,2,3])      #  Report errors , Like a dictionary   Cannot add mutable objects 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
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Collection Update

Can pass update() Method , Update another object to the existing collection , This process will also be de duplicated ：

>>> s = set([1,2,3,4,5])
>>> s.update("hello")                   #  take hello Take it apart and put it into the collection 
>>> s
{1, 2, 3, 4, 5, 'h', 'o', 'e', 'l'}
>>> s.update("hello")                   #  Still de weight 
>>> s
{1, 2, 3, 4, 5, 'h', 'o', 'e', 'l'}
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Remove elements

adopt remove(key) Method deletes the specified element , Or use pop() Method . Be careful , A collection of pop Method cannot set parameters , Delete the specified element ：

• set.remove()

>>> s = {1, 2, 3, 4, 5, 'h', 'o', 'e', 'l'}
>>> s.remove(1)                         #  Delete the element 
>>> s
{2, 3, 4, 5, 'h', 'o', 'e', 'l'}
>>> s.remove('h')                       #  Delete the element 
>>> s
{2, 3, 4, 5, 'o', 'e', 'l'}
>>> s.remove('www')                     #  If you delete a non-existent element, an error will be reported 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'www'
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• set.pop()

>>> s1 = set("hello world")
>>> s1.pop()
'h'
>>> s1.pop()
'd'
>>> s1.pop()            #  Note that random deletion 
'o'
>>> s1.pop(1)           #  Cannot delete by index , Because it is disorderly 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pop() takes no arguments (1 given)
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️ Be careful ： A collection cannot take out an element , Because the collection does not support subscript index or dictionary access through key value pairs ：

>>> s1
{' ', 'e', 'l', 'r', 'w'}
>>> s1[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object does not support indexing
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