python enumerate

>>> my_list=['a','b','c']
>>> for idx,val in enumerate(my_list,1):
...     print idx, val
... 
1 a
2 b
3 c


[root@wangzi]# cat a.txt
12  3
i2  2
aai b
23  9
[root@wangzi]# cat enumerate.py 
#!/usr/bin/python
# -*- coding: UTF-8 -*-
import sys
def parse_data(filename):
    with  open(filename,'r') as f:
        for lineno, line in enumerate(f,1):
            fields=line.split()
            try:
                 
                count=int(fields[1])
            except ValueError as e:
                print('Line {}:Parse error:{}'.format(lineno,e))
parse_data(sys.argv[1])
[root@wangzi]# python enumerate.py a.txt
Line 3:Parse error:invalid literal for int() with base 10: 'b'