import re
line ="[u'INVOICE# SMR/0038 f\"', u'', u'', u'']"
pattern = re.compile('invoice#\s+([A-Za-z]{3}/\d{1,5})', re.I)
print( re.findall(pattern, line) )
# get the first match
m = pattern.search(line)
if m:
	print(m.group(1))