find_free_uids_from_file.py

#!/usr/bin/python3
import os

def find_used_uids(file1):
    uidlist=[]
    fin = open(file1, 'rt', encoding="ISO-8859-1")
    occurence = 0
    while True:
        line = fin.readline()
        if not line:
            break
        t1 = line.split(':')
        uidlist.append(int(t1[2]))
    fin.close()
    uidlist.sort()
    return uidlist

def find_unused_uids(list1):
    length=len(list1)
    i=0
    while (i<=length-2):
        if (list1[i+1]-list1[i] > 1):
            difference=list1[i+1]-list1[i]
            j=1
            if (difference > j):
                lowerrange=list1[i]+j
                highestrange=list1[i]+difference-1
                print(lowerrange,'-',highestrange)
            elif (difference==2):
                print(list1[i]+1)
            '''
            while (j<difference):
                print(list1[i]+j)
                j=j+1
            '''
        i=i+1

    uidlimit=65535
    if (list1[length-1]<65535):
        print(list1[length-1]+1,'-','65535')

if __name__ == "__main__":
    file2=r"/etc/passwd"
    x=find_used_uids(file2)
    print(x)
    print("Following uid numbers are available for use.")
    find_unused_uids(x)