def is_ecalendar_crse(course_code):
    """Checks whether a given crse code matches the eCalendar crse format, code-900 (ccc-xxx or ccc-xxxcx)
    Rules:
    at least 7 char in length
    two sections separated by '-'
    first section is letters
    second is alphanumeric, first 3 are numbers
    """
    code = str(course_code)
    if len(code) < 7 or code[4] != '-':
        return False
    code = code.split('-')
    return code[0].isalpha() and code[1].isalnum() and code[1][:3].isdigit()