>>> s="abc123abc"
>>> t= "".join([x for x in s if x.isdigit()]+[x for x in s if not x.isdigit()])
>>> print t
123abcabc
>>>

import os
import re
pattern = re.compile(r"abc(\d+)abc")
tree = os.walk("/path/to/ur/dir")
targets = []
for dirpath, dirnames, names in tree:    
for name in names:
        m = pattern.match(name)
        if m:
                newname = os.path.join(dirpath, "%sdfghij" % m.group1))                
                os.rename(os.path.join(dirpath, name), newname)

file_list = [
'list_nonunique1.py',
'Gene_read1.pyw',
'wx_psutil1.pyw',
'pa16names.txt',
'wxFrame_centerthings1.pyw',
'averagewords1.py',
'oneline.txt',
'tk_coinflip.pyw']
 
# replace extension .pyw with .py
new_list= []
for fname in file_list:
    if '.pyw' in fname:
        fname = fname[:-3] + 'py'
    new_list.append(fname)
    print(fname)
 
"""
my result -->
list_nonunique1.py
Gene_read1.py
wx_psutil1.py
pa16names.txt
wxFrame_centerthings1.py
averagewords1.py
oneline.txt
tk_coinflip.py
"""

old_file_name = 'bc13abc2.txt'
 
## This assumes there is only one "." in the file name
substrs = old_file_name.split(".")
print substrs
## then use siddhant3s' example to find the digits, or some way
## using isdigit() and add substrs[1] (the ending) to that name.
digits_list = [x for x in old_file_name if x.isdigit()]
print digits_list
 
## which is the same as
second_list = []
for x in old_file_name:
   if x.isdigit()
      second_list.append(x)
 
## you then have to .join into a string