Simplest way of checking for string that contains a string in list? [duplicate]

Yes, use any():

if any(s in item for item in L):
    print 'string was found!'

As the docs mention, this is pretty much equivalent to your function, but any() can take generator expressions instead of just a string and a list, and any() short-circuits. Once s in item is True, the function breaks (you can simply do this with your function if you just change retVal = True to return True. Remember that functions break when it returns a value).

You should avoid naming strings str and lists list. That will override the built-in types.