Python类调用onVideo()报TypeError:缺少self参数的解决求助

我跟着YouTube教程做目标检测软件，到10分钟时卡壳了。加了自己的测试视频验证代码，运行时报错：

TypeError: onVideo() missing 1 required positional argument: 'self'

我对Python类的用法不太熟，明明创建了Detector类的实例，调用onVideo()还是触发这个错误，贴出相关代码和错误栈，求解决这个TypeError。

Detector类代码 #

import cv2
import numpy as np
import time

class Detector:
    def __init__(self, videoPath, configPath, modelPath, classesPath):
        self.videoPath = videoPath
        self.configPath = configPath
        self.modelPath = modelPath
        self.classesPath = classesPath

        self.net = cv2.dnn_DetectionModel(self.modelPath, self.configPath)
        self.net.setInputSize(320,320)
        self.net.setInputScale(1.0/127.5)
        self.net.setInputMean((127.5, 127.5, 127.5))
        self.net.setInputSwapRB(True)

        self.readClasses()

    def readClasses(self):
        with open(self.classesPath, 'r') as f:
            self.classesList = f.read().splitlines()

        self.classesList.insert(0, '__Background__')
        self.colorList = np.random.uniform(low=0, high=255, size=(len(self.classesList), 3))

    def onVideo(self):
        cap = cv2.VideoCapture(self.videoPath)

        if not cap.isOpened():
            print("Error opening the file...")
            return
        
        success, image = cap.read()
        while success:
            classLabelIDs, confidences, bboxs = self.net.detect(image, confThreshold=0.4)
            bboxs = list(bboxs)
            confidences = list(np.array(confidences).reshape(1, -1)[0])
            confidences = list(map(float, confidences))
            bboxIdx = cv2.dnn.NMSBoxes(bboxs, confidences, score_threshold=0.5, nms_threshold=0.2)

            if len(bboxIdx) != 0:
                for i in range(len(bboxIdx)):
                    bbox = bboxs[np.squeeze(bboxIdx[i])]
                    classConfidence = confidences[np.squeeze(bboxIdx[i])]
                    classLabelID = np.squeeze(classLabelIDs[np.squeeze(bboxIdx[i])])
                    classLabel = self.classesList[classLabelID]
                    classColor = [int(c) for c in self.colorList[classLabelID]]

                    displayText = "{}:{:.2f}".format(classLabel, classConfidence)
                    x, y, w, h = bbox
                    cv2.putText(image, displayText, (x, y-10), cv2.FONT_HERSHEY_PLAIN, 1, classColor, 2)
                    cv2.rectangle(image, (x, y), (x+w, y+h), color=classColor, thickness=1)

            cv2.imshow("Result", image)
            key = cv2.waitKey(1) & 0xFF
            if key == ord("q"):
                break
            success, image = cap.read()
        cv2.destroyAllWindows()

主程序代码 #

from Detector import *
import os

def main():
    videoPath = "test_videos/gamevid.mp4"
    configPath = os.path.join("model_data", "ssd_mobilenet_v3_large_coco_2020_01_14.pbtxt")
    modelPath = os.path.join("model_data", "frozen_inference_graph.pb")
    classesPath = os.path.join("model_data", "coco.names")

    detector = Detector(videoPath, configPath, modelPath, classesPath)
    detector.onVideo()

if __name__ == '__main__':
    main()

错误信息 #

Traceback (most recent call last):
  File "c:\Users\mondo\Desktop\Final DT software\real_time_object_detection_cpu-main\model_data\DetectorMain.py", line 12, in main
    Detector.onVideo()
TypeError: onVideo() missing 1 required positional argument: 'self'

问题原因 #

从错误栈能明确看到，你实际运行时调用的是Detector.onVideo()（直接调用类的方法），而非你贴出来的detector.onVideo()（用实例调用方法）。虽然你提供的主程序代码写法正确，但实际运行的代码肯定写错了，直接调用了类的方法，没有传入实例对象。

修复方案 #

1. 打开你的主程序文件DetectorMain.py，找到调用onVideo的代码行：
   • 把错误的Detector.onVideo()改成detector.onVideo()
   • 确保你是用之前创建的实例detector来调用方法，而不是类Detector本身
2. 保存修改后重新运行程序，错误即可解决。

补充说明 #

Python中，类的实例方法（比如onVideo）第一个参数必须是self，它代表类的实例本身。当你用实例调用方法时，Python会自动把实例作为self参数传入；但如果直接用类调用方法，就需要手动传入实例，否则就会报缺少self参数的错误。

内容的提问来源于stack exchange，提问作者Charlie