I want to create a list from an existing list after removing all duplicates. Program works if I use a "for loop" but nothing happens if I use a list comprehension.
#use for loop
l=[1,2,2,3,1,1,2]
j=[]
for i in l:
if i not in j:
j.append(i)
print l
print j
#using list
l1=[1,2,2,3,1,1,2]
j1=[]
j1=[i for i in l1 if i not in j1]
print l1
print j1
The expression [i for i in l1 if i not in j1] is evaluated and then assigned to j1. So during the evaluation j1 stays empty.
BTW: An easy was of removing duplicates is to pass the list to the set function and then to the list function if you need a list:
j1=list(set(l1))
j1 is [] at the start and isn't updated at intermediate points within the list comprehension. Could do this instead of list comprehension though:
l1=[1,2,2,3,1,1,2]
j1=list(set(l1))
print l1
print j1
