wait (): flag True, execution effect is pass, the contrary is blocked (default is False)
print (e.is_srt) set method flag is set to True | clear the flag is set to False
e.is_set () can be set to True
wait method has a flag in the event
If this flag is the implementation of the results True, wait method is to pass
If this flag is the effect of False, wait method is blocked
Until this flag is changed to True
Control flag
A state determination flag is_set
set method flag is set to True
clear method flag is set to False