$ python
Python 2.5.1 (r251:54863, Jun 15 2008, 23:59:20) 
[GCC 4.1.2 20070925 (Red Hat 4.1.2-33)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.getlogin()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 2] No such file or directory
>>>

#include <stdio.h> 
#include <unistd.h> 

int main()
{
    printf(getlogin());

    return 0;
}

import os, pwd
def custom_getlogin():
    return pwd.getpwuid(os.getuid())[0]