In Python, it is very convenient to use list as the basic data type, and it is also one of the most common data structures in Python. So what should we do when performing reverse operations on the list? Let's take a look together below. First of all, it should be noted that when using list reverse order, it will automatically sort the elements, that is, arrange the elements in ascending order. So we can use a for loop in the list to perform reverse operations. When using the for loop, we first need to define a variable to store the result of the reverse order operation, and then use the for loop to traverse. After the traversal is complete, the data in reverse order can be obtained. The following is an example: If you want to perform a reverse order operation, you can write it like this: Note: In this example, a for loop is used to traverse the elements, so the final result is: After each traversal, the reversed order data will be stored into the variable. Final output result: As can be seen from the above example, the result obtained after executing the for loop is:
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1. Define variables
First of all, we need to define a variable, the name of this variable is called list, which is used to store the result of the reverse operation we want to perform. The variable name should be short, for example: In the above example, if we want to store the result of the reverse operation, we can write it like this: Of course, if we want more complicated usage, we can also use functions instead of variables. Example: Define this function as public static void main() in function()(): In the above example, we defined a variable named public static void main(). This variable is equivalent to a function. So when we call this function in the for loop, we can use it to get the result of the reverse operation. Example: In the above example, we used the string.split() function to generate an object named list.class.
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2. traverse
Traversal is a way to inspect elements, which allows us to know the order of elements and their position. Traversal can be divided into two types, sequential traversal and search traversal. In Python, sequential traversal is used a lot because it allows us to easily determine the position of an element. There are many ways to use for loop traversal in Python, for example: In addition, you can also use the sort () method to traverse, and use the sort () method to traverse each element in the list. Note: When using the sort() method, we should pay attention that it returns the sum of all elements in the list, not the list itself. In addition to using the sort () method, we can also use the list. additional () method to traverse. When traversing the array, we need to pay attention to the position of each element in the array and its order in the array. One final thing to note is that iterating over an array doesn't have to be done all at once. If we want to traverse the array once for each element in the array, we can sort the array before traversing the array. As you can see from the above example, the array itself does not need to be traversed during the traversal process. After sorting the array, the final result can be obtained. During traversal, we need to take care to arrange the array in ascending order.
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3. Data after reverse order
In the above example, we used the for loop to reverse the order of the list, so after each iteration, we will get a list. But this list is not the result we want, so we need to convert it to a string and store it in a variable. Lists can be reversed using strings in Python, so what should you do if you want to reverse the list? Then use a for loop to traverse each element in the list and store the reversed data in a variable. Finally, use the variable to print the result. As you can see from the above example, after traversing the list, you will get a string type of data. And this data is the result we want. So when printing, we only need to print out the string.
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4. Output the result
In the above example, we used the for loop to traverse the elements, so let's take a look at how to output the results when using the for loop to traverse the elements. For every function in Python, we have to test. First, confirm whether it is a static function, that is, whether it has a return value. The following is a test function in Python: Input parameter: result; Output parameter: return; Run the above code, you can see that the output result is: This shows that it is a static function. If you need to return a value, you can use the print statement to output the result. As can be seen from the above code, when the for loop is used to traverse elements, the reversed result will be stored in a variable after each traversal. We just need to assign values to variables.
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5. Summary
When using the for loop to traverse the list, you need to pay attention to the following points: (1) During the traversal process, use the for loop to traverse, and you can sort the elements in the list in ascending order. (2) For the elements to be reversed, if you do not use the for loop to traverse, you can directly use the list itself to perform the reverse operation, that is, directly use the list itself to traverse all the elements in the list. (3) For elements that need to be operated in reverse order, they can be stored in variables. (4) When using a for loop in a loop, it should be noted that after each loop traversal, the data in the variable needs to be updated. In each iteration, an update is made to the variable. (5) Note that the data size in the variable will not change. If the data is too large or too small, it will affect the efficiency of the loop. (6) If a list is used as a variable, all elements in the list should be set to NULL when using a for loop to traverse the list. In this way, no errors will occur when traversing.
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6. Practice questions
After learning the method of list reverse order, we can also use for loop to realize list reverse order operation. The following is a practice question, let's practice it together: Then use the for loop to traverse the list, after traversing, you can get the data in reverse order. The following is the output result: The above is the introduction to the method of reverse order of list. In Python, list is a basic data type, which can be used to store types such as strings, lists, and tuples. After learning the reverse order of list, everyone should have learned it, right? Learning summary: Through the above introduction, we can see that when using the list for reverse order, we can use the for loop to traverse. So we can also use it to process other types of data.
Commonly used python list reverse order code:
1. Use `reverse()` method:
```python
lst = [1, 2, 3, 4, 5]
lst.reverse()
print(lst) # output: [5, 4, 3, 2, 1]
```
2. Use slice operation:
```python
lst = [1, 2, 3, 4, 5]
new_lst = lst[::-1]
print(new_lst) # output: [5, 4, 3, 2 , 1]
```
3. Use `reversed()` function:
```python
lst = [1, 2, 3, 4, 5]
new_lst = list(reversed(lst))
print(new_lst) # output: [ 5, 4, 3, 2, 1]
```
4. Use `for` loop:
```python
lst = [1, 2, 3, 4, 5]
new_lst = []
for i in range(len(lst )-1, -1, -1):
new_lst.append(lst[i])
print(new_lst) # Output: [5, 4, 3, 2, 1]
```
5. Use list comprehension:
```python
lst = [1, 2, 3, 4, 5]
new_lst = [lst[i] for i in range(len(lst)-1, -1, -1)]
print(new_lst) # 输出：[5, 4, 3, 2, 1]
```