How to implement a OpenCV code on ROS Melodic

Question

I made on Ubuntu an OpenCV code to detect a person, now I'm trying to pass this code to ROS Melodic but this gives me the next error:

File "/ws/src/vision-car/scripts/yolo-cam.py", line 70
    cvzone.putTextRect(img,f"{currentClass} {conf}",(max(0,x1),max(35,y1)),scale=2,thickness=2)
                                                  ^
SyntaxError: invalid syntax

On Ubuntu 22.0.4 the code works on Python 3.10.6, I'm new to using this platform, ros and opencv, so I accept all types of tips.

My Python version: 3.6.9

I'm using Docker to run ROS

My code is:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String
from std_msgs.msg import Float32
from std_msgs.msg import Int32
from ultralytics import YOLO 
import cv2
import cvzone
import math
import numpy as np
#from sort import *

cap = cv2.VideoCapture(0) #Iniciamos la webcam
#Aqui ingresamos la resolucion de la webcam
cap.set(3, 1280) #3 indica ancho
cap.set(4,720) #4 indica alto

#cap = cv2.VideoCapture("sVideos/bikes.mp4") #For Video

model = YOLO("weights/yolov8n.pt") #Mandamos a llamar a los pesos predefinidos por YOLO

classNames = ["person", "bicycle", "car", "motorbike", "aeroplane", "bus", "train", "truck", "boat",
              "traffic light", "fire hydrant", "stop sign", "parking meter", "bench", "bird", "cat",
              "dog", "horse", "sheep", "cow", "elephant", "bear", "zebra", "giraffe", "backpack", "umbrella",
              "handbag", "tie", "suitcase", "frisbee", "skis", "snowboard", "sports ball", "kite", "baseball bat",
              "baseball glove", "skateboard", "surfboard", "tennis racket", "bottle", "wine glass", "cup",
              "fork", "knife", "spoon", "bowl", "banana", "apple", "sandwich", "orange", "broccoli",
              "carrot", "hot dog", "pizza", "donut", "cake", "chair", "sofa", "pottedplant", "bed",
              "diningtable", "toilet", "tvmonitor", "laptop", "mouse", "remote", "keyboard", "cell phone",
              "microwave", "oven", "toaster", "sink", "refrigerator", "book", "clock", "vase", "scissors",
              "teddy bear", "hair drier", "toothbrush"]

# Tracking
#tracker = Sort(max_age=20, min_hits=3, iou_threshold=0.3)

zone = "middle"

if __name__=='__main__':
    rospy.init_node("talker")
    rate = rospy.Rate(10)
    while True:
        succes, img = cap.read() #La funcion read regresa a succes si se recibio una imagen y a img la imagen recibida
        results = model(img, stream=True) #Comparamos las imagenes recibidas con los pesos
        
        detections = np.empty((0, 5))

        #El siguiente for dependiendo de las imagenes obtenidas muestra los rectangulos alrededor de los objetos escaneado
        for r in results:
            boxes = r.boxes
            for box in boxes:
                # Con opencv
                x1,y1,x2,y2 = box.xyxy[0] #Guardamos los valores de alto, ancho, x y y
                x1,y1,x2,y2 = int(x1), int(y1), int(x2), int(y2) #Convertimos los valores a ints
                #cv2.rectangle(img,(x1,y1),(x2,y2),(255,0,255),4) #Creamos los rectangulos de los objetos

                # Con cvzone
                w,h = x2-x1,y2-y1 #Guardamos los valores de alto, ancho, x y y
                #bbox = int(x1), int(y1), int(w), int(h) #Convertimos los valores a ints
                if classNames[0]:
                    print("x1= "+str(x1), "y1="+str(y1), "w="+str(w), "h="+str(h))
                # Confidence
                conf = math.ceil((box.conf[0]*100))/100 #Obtenemos el weight del objeto y lo redondeamos
                cls = int(box.cls[0])

                # Only detect persons
                currentClass = classNames[cls]
                if currentClass == "person" and conf > 0.3:
                    cvzone.cornerRect(img,(x1,y1,w,h), l=10, rt=5)#Creamos los rectangulos de los objetos
                    #Imprimimos el weight del objeto en una etiqueda encima del rectangulo del objeto
                    cvzone.putTextRect(img,f"{currentClass} {conf}",(max(0,x1),max(35,y1)),scale=2,thickness=2)

                    currentArray = np.array([x1,y1,x2,y2,conf])
                    detections = np.vstack((detections,currentArray))
        
                # Calculate the central pixel
                sup_izq,sup_der,inf_izq,inf_der = (x1),(x1+w),(x1),(x1+w)
                prom_pixel = (sup_izq+sup_der+inf_izq+inf_der)/4
                
                #  Generate the divisions on the screen
                if prom_pixel >= 0 and prom_pixel <= 426:
                    zone = "left"
                elif prom_pixel > 426 and prom_pixel < 854:
                    zone = "midle"
                else:
                    zone = "right"
                print(zone)
                
                #resultsTracker = tracker.update(detections)

                #for result in resultsTracker:
                    #x1,y1,x2,y2,id = result
                    #x1,y1,x2,y2 = int(x1), int(y1), int(x2), int(y2) #Convertimos los valores a ints
                    #print(result)
                    



        cv2.imshow("Image", img) #Mostramos lo que ve la webcam
        cv2.waitKey(1)

I tried updating pip, python, and the libraries, but idk why I got this error.

Answer 1

The issue is mainly versions you're running. ROS Melodic targets Ubuntu 18.04, so you'll need to use that distro. But the bigger issue is Melodic also targets Python2.7.

If you want to run ROS nodes with Python3 you'll need to use ROS Noetic and Ubuntu 20.04.