Python sort file based on last field

Input file:

$ cat file.txt
IN,90,453
US,12,1,120
NZ,89,200
WI,500
TS,12,124

Required output: Sort the above comma delimited file based on the last field (column). i.e. required output:

US,12,1,120
TS,12,124
NZ,89,200
IN,90,453
WI,500

Solution:
The solution using Awk in UNIX bash shell is here. And here is the python one:

$ python
Python 2.5.2 (r252:60911, Jan 20 2010, 21:48:48)
[GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> d_list = [line.strip() for line in open("file.txt")]
>>> d_list
['IN,90,453', 'US,12,1,120', 'NZ,89,200', 'WI,500', 'TS,12,124']
>>> d_list.sort(key = lambda line: line.split(",")[-1])
>>> d_list
['US,12,1,120', 'TS,12,124', 'NZ,89,200', 'IN,90,453', 'WI,500']
>>> for line in d_list:
...     print line
...
US,12,1,120
TS,12,124
NZ,89,200
IN,90,453
WI,500
>>>

Some notes:
Accessing last element of a list in python:
A negative index accesses elements from the end of the list counting backwards. The last element of any non-empty list is always list[-1].

Remove all except digits using python

Input file:

$ cat file.txt
4590:21333 2ewwq13232
12ada1212w1 1
13224 9#09io#
qw2323000 9023

Required: From the above file only keep the digits (i.e. remove all other characters except digits)

Way1: Using python Regular Expression special character '\D' which matches any non-digit character (equivalent to the set [^0-9])

$ python
Python 2.5.2 (r252:60911, Jul 22 2009, 15:35:03)
[GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu3)] on linux2
>>> import re
>>> for line in open('file.txt'):
...     re.sub("\D", "",line)
...
'459021333213232'
'12121211'
'13224909'
'23230009023'
>>>

Another way : Using python filter built-in function to iterate isdigit() on all lines of the file.

>>>
>>> for line in open('file.txt'):
...     filter(lambda x: x.isdigit(), line)
...
'459021333213232'
'12121211'
'13224909'
'23230009023'
>>>

Python - Adding numbers in a list

Lets see some of ways in python to add the numbers present in a list.

Suppose:

>>> numlist = [10,20,5,30]
>>> numlist
[10, 20, 5, 30]
>>> print sum(numlist)
65

Using python built in function 'reduce'

>>> numlist
[10, 20, 5, 30]
>>> def add(x, y): return x + y
...
>>> sum = reduce(add, numlist)
>>> sum
65

Enhancing the above using python 'lambda' function

>>> numlist
[10, 20, 5, 30]
>>> reduce(lambda b,a: a+b, numlist)
65
>>>

Or using python for loop:

>>> numlist
[10, 20, 5, 30]
>>> sum = 0
>>> for i in numlist:
...     sum += i
...
>>> sum
65
>>>