python - String to Integer error on file name -

i'm trying add 59 3 digits in specific position in files in folder, gives error:

valueerror: invalid literal int() base 10: ''

i have checked prints, , indeed 3 char string, containing digits(by looks)

code :

import os  def left(s, amount):         return s[:amount]  def right(s, amount):         return s[-amount:]  def mid(s, offset, amount):         return s[offset:offset+amount]   filename in os.listdir("v:\hd_raster\cta2-gua3"):         s = mid(filename, 21, 3)         print("chars : " + len(s) + " string : " + s)         s = int(s) + 59         s = string(s)            os.rename(filename,left(filename,21) +  s + mid(filename,24,len(filename)) 

folder screenshot of file names :

your code fragile, , functions left, mid, , right suggest more used language.

among other things, works if current directory contains files, because listdir returns file name, not it's path. os.rename fail.

try making little more flexible , bulletproof.

import glob import os  fpath = r"v:\hd_raster\cta2-gua3" file_prefix= 'trans_leilao-004-14_0' full_prefix = os.path.join(fpath,prefix) prefix_len = len(full_prefix)  files = glob.glob(full_prefix+r"???.*") old_file in files:     n = old_file[prefix_len:prefix_len+3]     try:         new_n = int(n) + 59     except valueerror:         print "failed parse filename: " + old_file         continue     new_file = old_file[:prefix_len] + str(new_n) + old_file[prefix_len+3:]     try:         os.rename(old_file, new_file)     catch oserror:         print "failed rename " + old_file