python can't find file it just made

python can't find file it just made

My program cannot find the path that it just made, the program is for
sorting files in the download folder. If it finds a new type of file it
should make a folder for that file type.
import os
FileList = os.listdir("/sdcard/Download/")
for File in FileList:
#print File
extension = ''.join(os.path.splitext(File)[1])
ext = extension.strip('.')
if os.path.exists("/mnt/external_sd/Download/" + ext):
Data = open("/sdcard/Download/" + File, "r").read()
file("/mnt/external_sd/" + ext + "/" + File, "w").write(Data)
elif os.path.exists("/mnt/external_sd/Download/" + ext) != True:
os.makedirs("/mnt/external_sd/Download/" + ext)
Data = open("/sdcard/Download/" + File, "r").read()
file("/mnt/external_sd/" + ext + "/" + File, "w").write(Data)