import re

r = re.compile(r"Prompt:(?![ \t]*\n)")

# Doesn't match because no text between Prompt: and \n
s = 'Prompt: \n'
m = r.search(s)
if m:
	print "m: " + m.group(0)

# Matches because text exists between Prompt: and \n
s2 = 'Prompt: Something\n'
m2 = r.search(s2)
if m2:
	print "m2: " + m2.group(0)