comparing two lists

[jimgardener]

hi
I have two lists of names.I need to find the difference between these
two lists.I tried to do it using sets.But I am wondering if there is a
better way to do it.Please tell me if there is a more elegant way.
thanks,
jim

my code snippet follows..

oldlst=['jon','arya','ned','bran']
newlst=['jaime','jon','cersei']

newlyadded=set(newlst)-set(oldlst)
removed=set(oldlst)-set(newlst)
unchanged=set(oldlst)& set(newlst)
print '%d were newly added= %s'%(len(newlyadded),list(newlyadded))
print '%d were removed=%s'%(len(removed),list(removed))
print '%d were unchanged=%s'%(len(unchanged),list(unchanged))

this produces the output
--------------
2 were newly added= ['jaime', 'cersei']
3 were removed=['ned', 'arya', 'bran']
1 were unchanged=['jon']

[Vlastimil Brom]

2010/3/5 jimgardener <jimga...@gmail.com>:

> --
> http://mail.python.org/mailman/listinfo/python-list
>

Hi,
I guess for lists with unique items and order insignificant this is
just fine; you may also check difflib, if it suits your needs; there
are multiple comparing and displaying possibilities, e.g.:

>>> import difflib
>>> print "\n".join(difflib.unified_diff(['jon','arya','ned','bran'], ['jaime','jon','cersei']))
---

+++

@@ -1,4 +1,3 @@

+jaime
jon
-arya
-ned
-bran
+cersei
>>>

hth,
vbr

[Terry Reedy]

On 3/5/2010 3:05 AM, jimgardener wrote:
> hi
> I have two lists of names.I need to find the difference between these
> two lists.I tried to do it using sets.But I am wondering if there is a
> better way to do it.Please tell me if there is a more elegant way.
> thanks,
> jim
>
> my code snippet follows..
>
> oldlst=['jon','arya','ned','bran']
> newlst=['jaime','jon','cersei']
>
> newlyadded=set(newlst)-set(oldlst)
> removed=set(oldlst)-set(newlst)
> unchanged=set(oldlst)& set(newlst)

Except for the duplicate calls to set, this is fine. If order and
duplication are irrelevant (and hashability is guaranteed), use sets to
start with.