Appending unique part of string to list

Question

I have following code from which I expect the output as : ['abcdef'] ['def']. I want the a2 list to contain unique elements of a1 that are not present in variable x.

>>> a1=[]
>>> a2=[]
>>> a1.append("abcdef")
>>> x="abc"
>>> if x not in a1:
...     a2.append(a1)
... 
>>> print a1, a2
['abcdef'] [['abcdef']]

Any help is appreciated.

This question is NOT a duplicate of Appending an id to a list if not already present . My question deals with appending a substring.

You should add some better examples, currently it's not clear what you're doing here. — Ashwini Chaudhary, May 14 '14 at 07:17
I think Omer's answer below is correct. The `unique elements of ...` points to that. If so, you should know that _substring_ is the wrong word for it. You're looking at strings as sets of characters. And, I'm getting `['abcdef']` and `[]` from your code since the `if` statement is false. — keyser, May 14 '14 at 07:20

score 1 · Accepted Answer · answered May 14 '14 at 07:18

this should work. you need to compare each letters one by one then append them to a new string

a1=[]
a2=[]
a1.append("abcdef")
x="abc"
y = "abcdef"
new = ""
for letter in y:
    if letter not in x:
        new = new + letter

a2.append(new)

print a1, a2

output:

['abcdef'] ['def']
[Finished in 0.0s]

this version will check each item in the list vs a single string to check if the string is in any of those

a1=[]
a2=[]
a1.append("abcdef")
x="abc"
new = ""
for item in a1:
    for letter in item:
        if letter not in x:
            new = new + letter

a2.append(new)

print a1, a2

Nice interpreting of the question. I did not get this :) – keyser May 14 '14 at 07:20 — keyser, May 14 '14 at 07:20

score 0 · Answer 2 · answered May 14 '14 at 07:28

If you really only care about unique letters, you can do this very easily using sets:

>>> set('abcdef') - set('def')
{'a', 'b', 'c'}

If you need the answer as a string, then you can do ''.join(set('abcdef') - set('def').

Note that this doesn't keep the elements in any particular order (they happen to be alphabetical here, but the internal order of a set is arbitrary).

Appending unique part of string to list

2 Answers2