With ipython you can write a function, like:

prompt [1]# def parse(line):
    ip, host = line.split()
    return "{host} IN PTR {ip}".format(host=host,ip=ip)

To edit our function, just use %edit and reference the line

prompt [2]# %edit 1

Once you modify the function, you cannot reference the newer code with edit, as

prompt [3]# %edit 2

just references “%edit 1” and not the newer code.

In this case we can simply recover the last code of our function with

prompt [4]# from inspect import getsourcelines
prompt [5]# getsourcelines(parse)
(['def parse(line):\n',
'    ip, host = line.split()[:2]\n',
'    return "{host} IN PTR {ip}".format(host=host,ip=ip)\n'],
1)