The common operations of lists in python combing summary (II)

Common operations on lists in python

Indexing and Slicing Lists

What is an index?

Strings, lists, and tuples are indexed

The index is the position of the element recorded from the leftmost, expressed as a number, starting from 0

Maximum index of string, list, tuple = length - 1

list = ['xiaoming', 'xiaohong']
print(list[0])  # 0is the index value，Returns the index value0corresponding element

What's a slice?

Indexes are used to access a single element, while slices access a range of elements

The slice looks up the elements between the two indexes that are separated by a colon inside the middle parentheses, as in[0: 10]

The slicing rules arekeep one's fingers crossed

list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(list[1: 3])  # Returns a list of elements corresponding to index values 1 to 3 (excluding 3)
print(list[:])  # with nothing on either side of the colon returns a list of all the elements)
print(list[0:])  # This also returns a list of all elements
print(list[:-1])  # Returns a list of all elements except the last one. The rightmost index is -1, followed by -2, and -3, if indexed from right to left.
print(list[::-1])  # Returns a reverse-ordered list
print(list[-3:-1])  # Returns a list of the 2nd and 3rd elements from the right to the left (indexed at -2, -3), since the slicing rule is left inclusive, right exclusive, so it will not contain elements indexed at -1
print(list[1:3:2])  # 2 represents the step size, jumping to get a list of elements
print(list[0:0]) # Returns an empty list

Attention:The list generated after slicing is a new list (even if, like the original list, it is a new variable)

Example:

List assignment by index/slice and index fetching

list[index] = new_item
list[0:2] = [1, 2]

Data can only be modified within the scope of an existing index, and cannot be assigned by adding a new index.

The index() function can be used to find the index value of the corresponding element.

Example:

The pop function removes elements

Remove and fetch elements of a list by index

(index)  # indexis the index of the element you want to delete，and returns the element at that index

Report an error if the passed-in index does not exist:

Direct deletion, no return value

del list[index]  # indexis the index of the element you want to delete

If the index does not exist, an error is reported:

Indexing & slicing specialization in tuples

Identity:

Tuples and lists alike get indexes and slice indexes
The index function is used in tuples in the same way as it is used in lists.

Specificity:Tuples cannot be indexed to modify and delete elements

String indexing and slicing

Each character of a string corresponds to an index, and the indexing rules are the same as for lists.

Strings are also sliced in the same way as lists

Attention:Strings cannot be modified or deleted by indexing, and strings cannot be modified.

String find () and index () function

Gets the index position of the element:

(item)  # Return the index of the item element, if item is more than one character, then return the index of the first character.
(item)  # # come (or go) backitemIndex of the element,in the event thatitemis more than one character，则come (or go) back第一个字符的索引

The difference between the two functions:find function can not get, will return -1; index function if you can not find, directly report errors

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