Introduction to Python's method of implementing list and mutual conversion between list and array

This article mainly introduces the list in Python and the implementation method of mutual conversion between list and array. It briefly analyzes the function and usage of list in Python and the implementation skills of mutual conversion between list and array. Friends in need can refer to it

The example in this article describes the implementation method of list and mutual conversion between list and array in Python. Share it with everyone for your reference, the details are as follows:

The list in python is an ordered collection, and elements can be added or deleted at any time;

# -*- coding: utf-8 -*-
frameID = 1
frameID_list = []
frameID_list.append(frameID)
print (frameID_list)
frameID = 2
frameID_list.append(frameID)
print (frameID_list)
name = 'SRX'
frameID_list.append(name)
print (frameID_list)
print (len(frameID_list))  #打印长度
print (frameID_list[2])  #使用[]进行索引
print (frameID_list[-1])
frameID_list.insert(1, 'WJC')  #在指定位置插入元素
print (frameID_list)
frameID_list.pop()  #将最后一位的元素删除
print (frameID_list)
frameID_list.pop(0)  #删除指定位置的元素
print (frameID_list)

The following is said Let's convert list to array in numpy.

First of all, the attributes of the elements in the list should be consistent before conversion, as shown below. The elements contained in frame_ID_list are the frame numbers recorded in str type. First, use np.array to convert it into an array of int type, and then A mathematical operation is performed on each element of the converted array. Since the result of the operation is float, it is forced to be converted to int type in the second line. Finally, the np array is converted back to list. The entire operation It is equivalent to completing the process of performing mathematical operations on each element in the list (which contains elements of type str) and then converting it back to the list.

frame_ID_list_np = np.array(frame_ID_list, dtype = int)
frame_ID_list_np = np.array(frame_ID_list_np / 1000 * fps, dtype = int)
frame_ID_list = frame_ID_list_np.tolist()

In addition, there is another point that needs attention, that is, when judging whether two variables are equal after type conversion, for example:

frame_ID = '1000'
ID_count = 1000
frame_ID = '1000'
ID_count = 1000
if frame_ID == ID_count:
　　...

At this time, this if will not be established. It is easy to see the error by writing it directly. However, when frame_ID and ID_count are obtained from other variables, it is not so clear to see the two. type, so be sure to pay attention to these small details when programming;

is similar when storing files, such as:

##

str_name_FID = str(frame_ID_list_np_save[count_save_frame_np])
cv2.imwrite('image/' + video_name_save + '_' + str_name_FID + '.jpg',frame) #save the image
count_save_frame_np = count_save_frame_np + 1

When storing pictures, the names of the pictures must be str type strung together. count_save_frame_np is an int type variable. If you use this variable directly as part of the picture name in the program, no file will be saved, so The forced conversion of the first line is necessary. Just convert it into str type first and then use it.

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