remove the flush=True argument

it causes a failure in Circuitpython

Author: Pascal Deneaux

examples/pn532_simpletest.py

@@ -48,7 +48,7 @@
 while True:
     # Check if a card is available to read
     uid = pn532.read_passive_target(timeout=0.5)
-    print('.', end="", flush=True)
+    print('.', end="")
     # Try again if no card is available.
     if uid is None:
         continue