Python實現將一個文件夾下面的多個txt文件合併成一個txt文件

import os
import shutil  #導入這個包
txtpath='/CNN/txtpath'
namelist=[x for x in os.listdir(txtpath)]
namelist.sort(key=lambda x:int(x[:-4]))   #txt file name
print len(namelist)#1674
outfilename='/CNN/b.txt'
outfile=open(outfilename,'a')#a沒有文件可以創建
for i in range( len(namelist) ):
	datapath = os.path.join(txtpath, namelist[i])
	print datapath
	file=open(datapath,'r')
	shutil.copyfileobj(file,outfile)
	file.close()
outfile.close()