Ok, with your help (the backslash was the issue), here's what I could come up with
pattern = re.compile(r'([\w\-]+)(?=(\s*install\s*))', re.MULTILINE)
matches = re.finditer(pattern, string_to_analize)
for match in matches:
print match.group()
which does exactly what is needed.
Thanks a lot for your help ! ;)
PS : Just a very strange thing : that regex does not function on the website, do you understand why ? http://regex101.com/r/iM2gJ1