Learning python III: lists, tuples, dictionaries, collections

Lists, tuples, dictionaries, collections

List

Use nested lists to create another list that is in the list, such as:

>>>a = ['a', 'b', 'c']
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[['a', 'b', 'c'], [1, 2, 3]]
>>> x[0]
['a', 'b', 'c']
>>> x[0][1]
'b'
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related functions:

function	description
`list(seq)`	Convert a list of tuples
`len(list)`	The number of list elements
`list.append(obj)`	Add new object at the end of the list
`list.count(obj)`	The number of times an element statistics appear in the list
`list.extend(seq)`	A plurality of values in another sequence added at the end of the list of one-time (with a new list of the original extended list)
`list.pop([index=-1])`	Removing one element in the list (default to the last element), and returns the value of the element
`list.remove(obj)`	Remove the list a value of the first match
`list.reverse()`	Reverse elements in the list
`list.sort( key=None, reverse=False)`	The original list is sorted
`list.clear()`	clear the list
`list.copy()`	Copy List

Tuple

Elements of a tuple can not be changed. Tuples use parentheses, square brackets list .

>>>tup1 = ('Google', 'Runoob', 1997, 2000);
>>> tup2 = (1, 2, 3, 4, 5 );
>>> tup3 = "a", "b", "c", "d";   # 不需要括号也可以
>>> type(tup3)
<class 'tuple'>

tup1 = (); # 创建空元组
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When tuple contains only one element, the element needs to be added after the comma, or brackets will be used as the operator:

>>>tup1 = (50)
>>> type(tup1)     # 不加逗号，类型为整型
<class 'int'>
 
>>> tup1 = (50,)
>>> type(tup1)     # 加上逗号，类型为元组
<class 'tuple'>
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Element value tuples can not be deleted, but we can use the del statement to delete an entire tuple, the following examples:

#!/usr/bin/python3
 
tup = ('Google', 'Runoob', 1997, 2000)
 
print (tup)
del tup;
print ("删除后的元组 tup : ")
print (tup)

------------------------------------------

删除后的元组 tup : 
Traceback (most recent call last):
  File "test.py", line 8, in <module>
    print (tup)
NameError: name 'tup' is not defined
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tuple(seq)Convert list is a tuple. Distinguished list(seq)is to convert a tuple into a list. Following examples:

>>> list1= ['Google', 'Taobao', 'Runoob', 'Baidu']
>>> tuple1=tuple(list1)
>>> tuple1
('Google', 'Taobao', 'Runoob', 'Baidu')
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dictionary

Twice is not allowed the same key. When you create is assigned if the same key twice, the last value will be remembered, the following examples:

#!/usr/bin/python3
 
dict = {'Name': 'Runoob', 'Age': 7, 'Name': '小菜鸟'}
 
print ("dict['Name']: ", dict['Name'])

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Key must be immutable, it may be numbers, strings, or act as a tuple, and will not work with the list, the following examples:

#!/usr/bin/python3
 
dict = {['Name']: 'Runoob', 'Age': 7}
 
print ("dict['Name']: ", dict['Name'])

--------------------------------------

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    dict = {['Name']: 'Runoob', 'Age': 7}
TypeError: unhashable type: 'list'
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str(dict) Output dictionary, printable string representation.

>>> dict = {'Name': 'Runoob', 'Age': 7, 'Class': 'First'}
>>> str(dict)
"{'Name': 'Runoob', 'Class': 'First', 'Age': 7}"
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function	description
`radiansdict.fromkeys()`	Create a new dictionary, a sequence of elements do seq dictionary key, val is a dictionary of all the key corresponding to the initial value
`radiansdict.values()`	Returns an iterator, you can use list () to convert to the list
`pop(key[,default])`	Remove dictionary given key corresponding to the key value, the return value is deleted. key value must be given. Otherwise, return default values.
`popitem()`	Random return and remove the pair of keys and values of the dictionary (the end of the general deletion).

set

A set of basic operations:

Additive element
added to the collection element x s, if existing elements, nothing is done.s.add( x )

>>>thisset = set(("Google", "Runoob", "Taobao"))
>>> thisset.add("Facebook")
>>> print(thisset)
{'Taobao', 'Facebook', 'Google', 'Runoob'}
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Another method, elements may be added, and the parameter may be a list of tuples, dictionaries, syntax is as follows: s.update( x )X may be a plurality, separated by commas.

>>>thisset = set(("Google", "Runoob", "Taobao"))
>>> thisset.update({1,3})
>>> print(thisset)
{1, 3, 'Google', 'Taobao', 'Runoob'}
>>> thisset.update([1,4],[5,6])  
>>> print(thisset)
{1, 3, 4, 5, 6, 'Google', 'Taobao', 'Runoob'}
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The removable element is removed from the collection element x s, if the element does not exist, an error occurs. s.remove( x )

>>>thisset = set(("Google", "Runoob", "Taobao"))
>>> thisset.remove("Taobao")
>>> print(thisset)
{'Google', 'Runoob'}
>>> thisset.remove("Facebook")   # 不存在会发生错误
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'Facebook'
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In addition there is a method to remove elements in the collection, and if the element does not exist, an error does not occur. Format is as follows:s.discard( x )

>>>thisset = set(("Google", "Runoob", "Taobao"))
>>> thisset.discard("Facebook")  # 不存在不会发生错误
>>> print(thisset)
{'Taobao', 'Google', 'Runoob'}
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We can also set up a random element to delete the collection, syntax is as follows: s.pop()

thisset = set(("Google", "Runoob", "Taobao", "Facebook"))
x = thisset.pop()
print(x)
$ python3 test.py 
Runoob
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Repeating the test results are not the same. However, in the interactive mode, pop is the first element (the first element of the collection sorted) to delete the collection.

>>>thisset = set(("Google", "Runoob", "Taobao", "Facebook"))
>>> thisset.pop()
'Facebook'
>>> print(thisset)
{'Google', 'Taobao', 'Runoob'}
>>>
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Reproduced in: https: //juejin.im/post/5cf625a5f265da1bc14b156d