Tensorflow 2.0 is required, so if you don't have it, uncomment and run the following command

#!pip install tensorflow --upgrade

Download the weight file for YOLOv3 from their official website

!wget https://pjreddie.com/media/files/yolov3.weights

Prepare the folder for storing the weights

!rm -rf checkpoints

!mkdir checkpoints

Import all required libraries

import cv2
import numpy as np
import tensorflow as tf

from absl import logging
from itertools import repeat

from tensorflow.keras import Model
from tensorflow.keras.layers import Add, Concatenate, Lambda
from tensorflow.keras.layers import Conv2D, Input, LeakyReLU
from tensorflow.keras.layers import MaxPool2D, UpSampling2D, ZeroPadding2D
from tensorflow.keras.regularizers import l2
from tensorflow.keras.losses import binary_crossentropy
from tensorflow.keras.losses import sparse_categorical_crossentropy

Check TensorFlow version. It should be 2.0.

print(tf.__version__)

Define some imporant value which we will use later

yolo_iou_threshold   = 0.6 # iou threshold
yolo_score_threshold = 0.6 # score threshold

weightsyolov3 = 'yolov3.weights' # path to weights file
weights= 'checkpoints/yolov3.tf' # path to checkpoints file
size= 416             #resize images to\
checkpoints = 'checkpoints/yolov3.tf'
num_classes = 80      # number of classes in the model

List of layers in YOLOv3 FCN — Fully Convolutional Network

YOLO_V3_LAYERS = [
    'yolo_darknet',
    'yolo_conv_0',
    'yolo_output_0',
    'yolo_conv_1',
    'yolo_output_1',
    'yolo_conv_2',
    'yolo_output_2',
]