List of [python Basics] And pythonlist

List of [python Basics] And pythonlist

Python provides a data type called list, which can store an ordered set of elements.

Remember: A list can store data sets of any size. The list is a mutable object, which is different from the str class. The str class is an immutable object.

 

1. Create a list

List1 = list () # create an empty list list2 = list ([2, 3, 4]) # create a list that contains elements 2, 3, and 4list3 = list (["red ", "green"]) # create a string list list4 = list (range (3, 6) list5 = list ("abcd ")

 

We usually omit the brackets:

list1 = list[]list2 = list[2,3,4]

 

2. list common operations in python, the strings and lists are sequential types. A string is a string sequence, and a list is a sequence of any elements.

Common Operations of sequence (list) s

Operation	Description
X in s	Returns true if element x is in series s.
X not in s	Returns true if element x is not in s.
S1 + s2	Connect two sequences s1 and s2
S * n, n * s	N sequence s connections
S [I]	I element of sequence s
S [I, j]	Fragment of sequence s from subscript I to J-1 (list truncation)
Len (s)	The length of series s, that is, the number of elements in s.
Min (s)	Minimum element of sequence s
Max (s)	Maximum element of sequence s
Sum (s)	Sum of all elements in sequence s
For loop	In a for loop, the elements are reversed from left to right.
<, <=,>, >=, = ,! =	Compares two sequences. true is returned if it is true.
Random. shuffle (s)	Arrange elements in sequence s at will

3. if the subscript operator [] has a list mylist, the index in mylist [index] is the subscript of the list. Generally, the range of the lower mark is 0 to len (mylist)-1. mylist [index] is also called a subscript variable. Mylist [0], mylist [1]…… Access the list of 0th elements, the first element ...... Index can also be negative: mylist [-1], mylist [-2]… The first and second elements in the access list respectively ...... (If it is a negative number, the maximum value of the index is-1.) 4. The range of [start: end] mylst [start: end] to be intercepted is from start to end-1, forming a list.

>>>mylst= [0,1,2,3,4,5]>>>mylst[2,4][2, 3]

If start and end are omitted, start is 0 by default, and end is the last subscript of the list by default. start and end can also be negative, if the negative number is-n, replace it with-n + len (mylist ).

>>>mylist[:3][0, 1, 2]>>>mylist[2:][2, 3, 4, 5]>>>mylist[:][0, 1, 2, 3, 4, 5]>>>mylist[-4:-2][2, 3]

 

If start> end, mylist creates an empty list.

>>> Mylist [3: 2] # start> end, the error Traceback (most recent call last): File "<pyshell #1>", line 1, in <module> mylist [3: 2] NameError: name 'mylist' is not defined

 

5. List resolution list resolution consists of multiple square brackets, which contain an expression followed by a for clause, followed by 0 or more for or if clauses. For example:

>>>list1 = [x for x in range(5)]>>>list1[0, 1, 2, 3, 4]>>>list2 = [0.5*x for x in list1]>>>list2[0.0, 0.5, 1.0, 1.5, 2.0]>>>list3 = [x for x in list2 if x < 1.5]>>>list3[0.0, 0.5, 1.0]

 

6. List Method

Common list Methods

Append (x: object): None	Add the element to the end of the list
Count (x: object): int	Returns the number of times element x appears in the list.
Extend (lst: list): None	Append all elements in list l to list
Index (x: object): int	Returns the subscript of x that appears for the first time in the list.
Insert (index: int, x: object): None	Insert element x to the specified subscript in the list.
Pop (I): object	Delete the element at the given position and return it. Parameter I (Optional). If not specified, the last element in the list is deleted and returned.
Remove (x: object ): None	Delete the first x in the list
Reverse (): None	Reverse all elements in the list (not sorted)
Sort (): None	Sort the elements in the list in ascending order (Note: It is sort)

The above code is as follows:

>>> List1 = [2, 3, 4, 1, 32, 4] >>> list1.append (19) >>> list1 [2, 3, 4, 1, 32, 4, 19] >>> list1.count (4) 2 >>> list2 = [99, 54] >>> list2.extend (list1) >>> list2 [99, 54, 2, 3, 4, 1, 32, 4, 19] >>> list2.index (4) 4 >>> list2.insert (1, 25) >>> list2 [99, 25, 54, 2, 3, 4, 1, 32, 4, 19] >>> list2.pop () # Delete the last element 19 >>> list2 [99, 25, 54, 2, 3, 4, 1, 32, 4] >>> list2.pop (2) # Delete the element at the specified position, delete element 54 with subscript 2 >>> list2 [99, 25, 2, 3, 4, 1, 32, 4] >>> list2.remove (4) >>> list2 [99, 25, 2, 3, 1, 32, 4] >>> list2.reverse () # reverse the original sequence >>> list2 [4, 32, 1, 3, 2, 25, 99] >>> list2.sort () # Sort the original sequence in ascending order >>> list2 [1, 2, 3, 4, 25, 32, 99]