def deprecated(alternative=None):
    """This is a decorator which can be used to mark functions
    as deprecated. It will result in a warning being emitted
    when the function is used."""

    def real_decorator(func):
        @functools.wraps(func)
        def new_func(*args, **kwargs):
            msg = "Call to deprecated function {0}.".format(func.__name__)
            if alternative:
                msg += " Use {0} instead".format(alternative)
            warnings.warn_explicit(
                msg,
                category=DeprecationWarning,
                filename=compat.get_function_code(func).co_filename,
                lineno=compat.get_function_code(func).co_firstlineno + 1,
            )
            return func(*args, **kwargs)

        return new_func

    return real_decorator