Python 拼接很多图片变成格子大图

#!/usr/bin/python3
#encoding=utf-8
import numpy as np
from PIL import Image
import glob,os
if __name__=='__main__':
    files=glob.glob('100faces/*.png')
    num=len(files)
    filename_lens=[len(x) for x in files] #length of the files
    min_len=min(filename_lens) #minimal length of filenames
    max_len=max(filename_lens) #maximal length of filenames
    if min_len==max_len:#the last number of each filename has the same length
        files=sorted(files) #sort the files in ascending order
        pass
    else:#maybe the filenames are:x_0.png ... x_10.png ... x_100.png
        index=[0 for x in range(num)]
        for i in range(num):
            filename=files[i]
            start=filename.rfind('_')+1
            end=filename.rfind('.')
            file_no=int(filename[start:end])
            index[i]=file_no
        index=sorted(index)
        files=[prefix+'_'+str(x)+'.png' for x in index]
    print(files[0])
    baseimg=Image.open(files[0])
    sz=baseimg.size
    final_mat = []
    for i in range(0, 4):
        basemat=[]
        for j in range(6):
            file=files[i * 6 + j]
            im=Image.open(file)
            im=im.resize(sz,Image.ANTIALIAS)
            mat=np.atleast_2d(im)
            print(file)
            if len(basemat) == 0:
                basemat=np.atleast_2d(mat)
            else:
                basemat=np.append(basemat,mat,axis=1)
        if len(final_mat) == 0:
            final_mat=np.atleast_2d(basemat)
        else:
            final_mat=np.append(final_mat, basemat, axis=0)
    final_img=Image.fromarray(final_mat)
    final_img.save('merged_mix.png')