def get_usrname(user_uid):
    passwd_file = open('/etc/passwd')
    user_name_list = [passwd_file_line.split(':')[0] for passwd_file_line in passwd_file if passwd_file_line.split(':')[2] == user_uid]
    return user_name_list[0]
"""
## example /etc/passwd
psaftp:x:505:506:anonftp psa user:/:/sbin/nologin
apache:x:506:507:Apache server:/:/sbin/nologin
drweb:x:100:511:DrWeb system account:/var/drweb:/bin/false
webalizer:x:67:67:Webalizer:/var/www/usage:/sbin/nologin
mailman:x:41:41:GNU Mailing List Manager:/usr/lib/mailman:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
named:x:25:25:Named:/var/named:/sbin/nologin
sw-cp-server:x:507:512::/:/bin/true
paveln:x:10000:509::/var/www/vhosts/localhost.localdomain:/bin/false
nginx:x:498:497:Nginx user:/var/lib/nginx:/bin/false
test3:x:10001:10001::/home/test3:/bin/bash
test4:x:10002:10002::/home/test4:/bin/bash
testuser:x:10003:10003::/home/testuser:/bin/bash
testuser1:x:10003:10004::/home/testuser:/bin/bash
"""

def get_usrname(user_uid):
	for x in open('/home/rodegast/pass'):
		if x.split(':')[2] == user_uid:
			return x.split(':')[0]
print get_usrname("505")

user_uid = "506"
print map(lambda x: x.split(':')[0], filter(lambda x:x.split(':')[2] == user_uid, open('/home/rodegast/pass')))

def first(ls, test):
    for x in ls:
        if test(x):
            return x
def get_username(search_uid):
    with open('/etc/passwd') as inf:
        return first((passwd_file_line.split(':') for passwd_file_line in inf), lambda x: x[0] == search_uid)

lst = []
for elem in xrange(10):
    lst.append(elem)

lst = [elem for elem in xrange(10)]

import operator as op
 
split = lambda sep : lambda string : string.split(sep)
 
def find(item, seq, test=op.eq, key=lambda elt : elt):
    for elt in seq:
        if test(item, key(elt)):
            return elt
            
def get_username(uid):
    return find(uid,
                map(split(':'),
                    open('/etc/passwd')),
                key=op.itemgetter(2))[0]
 
print(get_username('10'))