Treehouse doesn't accept my code - already tested on my PC

COURSES = {
    "Python Basics": {"Python", "functions", "variables",
                      "booleans", "integers", "floats",
                      "arrays", "strings", "exceptions",
                      "conditions", "input", "loops"},
    "Java Basics": {"Java", "strings", "variables",
                    "input", "exceptions", "integers",
                    "booleans", "loops"},
    "PHP Basics": {"PHP", "variables", "conditions",
                   "integers", "floats", "strings",
                   "booleans", "HTML"},
    "Ruby Basics": {"Ruby", "strings", "floats",
                    "integers", "conditions",
                    "functions", "input"}
}


def covers(topic):
    return_list = []
    for x in COURSES:
        value = COURSES[x]
        intersect = value.intersection(topic)
        if len(intersect) >= 1:
            return_list.append(x)
    return return_list


def covers_all(topic):
    return_list = []
    for x in COURSES:
        value = COURSES[x]
        intersect = value.intersection(topic)
        if len(intersect) >= len(topic):
            return_list.append(x)
        return return_list