def wrapper(fn: typing.Callable):
if not hasattr(fn, '_depth'):
fn._depth = 0
@functools.wraps(fn)
def _inner(*args, **kwargs):
if fn._depth > n:
raise RuntimeError("call depth exceed %d" % n)
fn._depth += 1
try:
return fn(*args, **kwargs)
finally:
fn._depth -= 1
_inner._fn = fn
return _inner
