Finding elements not in a list
Your code is not doing what I think you think it is doing. The line for item in z:
will iterate through z
, each time making item
equal to one single element of z
. The original item
list is therefore overwritten before you've done anything with it.
I think you want something like this:
item = [0,1,2,3,4,5,6,7,8,9]
for element in item:
if element not in z:
print(element)
But you could easily do this like:
[x for x in item if x not in z]
or (if you don't mind losing duplicates of non-unique elements):
set(item) - set(z)
>> items = [1,2,3,4]
>> Z = [3,4,5,6]
>> print list(set(items)-set(Z))
[1, 2]
Using list comprehension:
print [x for x in item if x not in Z]
or using filter function :
filter(lambda x: x not in Z, item)
Using set
in any form may create a bug if the list being checked contains non-unique elements, e.g.:
print item
Out[39]: [0, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print Z
Out[40]: [3, 4, 5, 6]
set(item) - set(Z)
Out[41]: {0, 1, 2, 7, 8, 9}
vs list comprehension as above
print [x for x in item if x not in Z]
Out[38]: [0, 1, 1, 2, 7, 8, 9]
or filter function:
filter(lambda x: x not in Z, item)
Out[38]: [0, 1, 1, 2, 7, 8, 9]
list1 = [1,2,3,4]; list2 = [0,3,3,6]
print set(list2) - set(list1)