list1=[1,2,3,4]
list2=["qwe","asd","zxc"]
dictx={}
for x in range(len(list1)):
if x>len(list2):
    dictx[list1[x]]=None
else:
    dictx[list1[x]]=list2[x]

from itertools import chain, repeat

d = dict(zip(list1, chain(list2, repeat(None))))

import itertools
list1=[1,2,3,4]
list2=["qwe","asd","zxc"]
print ({l1:l2 for l1,l2 in itertools.izip_longest(list1,list2,fillvalue=None)})

import itertools
list1=[1,2,3,4]
list2=["qwe","asd","zxc"]
print ({l1:l2 for l1,l2 in itertools.zip_longest(list1,list2,fillvalue=None)})

{1: 'qwe', 2: 'asd', 3: 'zxc', 4: None}