Regex: Remove all match plus one char before all

[Alfalfa]

That is strange, I simply used a for loop and made an average, like so;

#!/usr/bin/python3
import re
import time

pattern = re.compile(r'[\w ]?\|BS\|')
buffer = "it |BS||BS||BS|this is one|BS||BS||BS|an example" #|BS| as in Backspace
test=time.time()

for x in range(0,100000):
   while re.search("\|BS\|", buffer):
       array = list(buffer)
       for m in re.finditer("\|BS\|", buffer):
           del array[m.start():m.end()]
           if m.start()-1 >= 0:
               del array[m.start()-1]
           buffer = ''.join(array)
           break
print(buffer)
print((time.time()-test)/100000)

I though it might be python 3 vs 2, altough with the example you provided I get similar results as what you just showed..
Anyhow, do you know how to fix the pattern in order to accept non-alphanumeric chars?