'RTC' object has no attribute 'alarm'

[Thosch42]

Hi all!
I'm pretty new to Python and the WiPy module. i received it last weekend and now I'm playin' arround.
I just want to set the WiPy periodically to sleep. But I get this confusing AttributeError. What's wrong?
Here's my code:

import machine
from machine import RTC
#import os
#import time

global counter
counter =0

def alarm_handler(rtc_o):
pass

print("\nWiPy is up\n")

rtc = RTC()
rtc.alarm(time=5000, repeat=True)
rtc_irq = rtc.irq(trigger=RTC.ALARM0, handler=alarm_handler, wake=machine.SLEEP)

while True:
print(counter)
counter = counter + 1
machine.sleep()