Save multiple images to one pdf using Pillow

save_as_pdf.py

from glob import glob
import os.path as path
from PIL import Image

def convert(img):
    '''Convert an RGBA image to an RGB image

    If the passed image has:
        img.mode == 'RGBA'
    then it will be converted to RGB.
    Else, the image itself will be returned.
        
    :PARAM: img - an object of type PIL.Image

    :RETURNS: img as RGBA
    '''
    if img.mode == 'RGBA':
        rgb = Image.new('RGB', img.size, (255,255,255)) 
        rgb.paste(img, mask=img.split()[3])
        return(rgb)
    else:
        return(img)

def save_as_pdf(files=None, out='images.pdf'):
    '''Save a list ofimage files as a concatenated pdf

    Take a list of images and save them to a pdf.
    One image per page, with no image compression

    :PARAM: files: list
        List of paths to images. 
        Tip: use glob to get these `glob(*.png)`
        If not passed, this fucntion will operate on all pngs in the current directory
    :PARAM: out: str
        Name of pdf to be saved

    :RETURNS: bool
        True if successful
    '''
    if files is None:
        files = glob('*.png') 
    else:
        for i in files:
            if not path.isfile(i):
                raise FileNotFoundError(f'{i} does not exist')

    if path.isfile(out):
        raise FileExistsError(f'{out} already exists.')

    images = [Image.open(i) for i in files]
    images = [convert(i) for i in images]
    images[0].save(
        out,
        'PDF',
        resolution=100.00,
        save_all=True,
        append_images=images[1:]
    )
    return(True)