s = "This be a string"
if s.find("is") == -1:
    print "No 'is' here!"
else:
    print "Found 'is' in the string."
    
if s.find("isX") == -1:
    print "No 'isX' here!"
else:
    print "Found 'isX' in the string."
s = "This be a string"
if s.find("is") == -1:
    print "No 'is' here!"
else:
    print "Found 'is' in the string."
    
if s.find("isX") == -1:
    print "No 'isX' here!"
else:
    print "Found 'isX' in the string."