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7.5.5 Event Objects

This is one of the simplest mechanisms for communication between threads: one thread signals an event and one or more other thread are waiting for it.

An event object manages an internal flag that can be set to true with the `set()` method and reset to false with the `clear()` method. The `wait()` method blocks until the flag is true.

`Event` ()
  The internal flag is initially false.

`isSet` ()
  Return true if and only if the internal flag is true.

`set` ()
  Set the internal flag to true. All threads waiting for it to become true are awakened. Threads that call `wait()` once the flag is true will not block at all.

`clear` ()
  Reset the internal flag to false. Subsequently, threads calling `wait()` will block until `set()` is called to set the internal flag to true again.

`wait` ([timeout])
  Block until the internal flag is true. If the internal flag is true on entry, return immediately. Otherwise, block until another thread calls `set()` to set the flag to true, or until the optional timeout occurs.

  When the timeout argument is present and not `None`, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof).