Combines several images into one PDF

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Python

I have this code that combines several images into one PDF file, and it was very good for some time, and then when merging images into a PDF file, it added an additional image to the images, which is the first image so that if I had four images, I found that he added a fifth image, which is a repetition of the image. The first and I don't know what the problem is, I tried several ways and I didn't succeed in that. I hope to get help with that.

import PIL
import os
import os.path
from PIL import Image

f = r'path'

li1 = []
count = 0
for file in os.listdir(f):
    f_img = f+"/"+file
    img = Image.open(f_img).convert('RGB')
    li1.append(img)
img.save(f+file+'.pdf', save_all=True, append_images=li1)

What I have tried:

I tried several modifications and it didn't help.