How to check whether a JPEG image is color or gray scale using only Python stdlib

I have to write a test case in Python to check whether a jpg image is in color or grayscale. Can anyone please let me know if there is any way to do it with out installing extra libraries like OpenCV?

You can check every pixel to see if it is grayscale (R == G == B)

from PIL import Image

def is_grey_scale(img_path):
    img = Image.open(img_path).convert('RGB')
    w, h = img.size
    for i in range(w):
        for j in range(h):
            r, g, b = img.getpixel((i,j))
            if r != g != b: 
                return False
    return True