import os


def get_bool(key, default="NO"):
    """
    Returns True if environment variable named KEY is one of
    "yes", "y", "t", "true" (lowercase of uppercase)

    otherwise returns False
    """
    env_var_value = os.getenv(key, default).lower()
    YES_VALUES = ("yes", "y", "1", "t", "true")
    if env_var_value in YES_VALUES:
        return True

    return False