Question

I need to match contents of a list with a given pattern, and form another list which will be having everything except the matches. Meaning, I am trying to make an exclude list.

Now with one pattern match, it is easy. But for more that one, it becomes tricky.

Lets see an example :

Lmain=[arc123, arc234,xyz111,xyz222,ppp999,ppp888]

for count in range(len[Lmain]):

    if Pattern matches Lmain[i]:
              Pass
    else:result.append(Lmain[i])

Now lets say pattern = arc , my result will be

result = [xyz111,xyz222,ppp999,ppp888]

This is just a logic, where I will be using regular expr for finding match.

Now if we have 2 patterns, then using above logic in a loop :

Pattern=['arc','xyz']

for pat in Pattern:
      if pat matches Lmain[i]:
          Pass
      else:result.append(Lmain[i])

This will give us the wrong result

result = [xyz111,xyz222,ppp999,ppp888,arc123,arc234,ppp999,ppp888]

So , you can see above logic just wont work .

My plan:

First we find exclude list for first Pattern which will give us result:

result = [xyz111,xyz222,ppp999,ppp888]

For 2nd pattern, we need to look in to the above result.

if Pattern matches Result[i]:
      Pass
else:result_final.append(Result[i])

I think we need to use Recursion to implement above logic. Now how do we do that?
Also we dont know the number of patterns user is going to enter. It can be one or more.

Anybody has any logic ideas, then please share.

Answer 1

Using a list comprehension and a generator expression, and skipping the intermediate step of building an exclude list and just building the final list:

>>> import re
>>> Lmain=['arc123', 'arc234', 'xyz111', 'xyz222','ppp999','ppp888']
>>> Pattern=['arc','xyz']
>>> [x for x in Lmain if not any(re.search(y, x) for y in Pattern)]
['ppp999', 'ppp888']