added chapter map to README

21-asyncio/spinner_asyncio.py

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+#!/usr/bin/env python3
+
+# spinner_asyncio.py
+
+# credits: Example by Luciano Ramalho inspired by
+# Michele Simionato's multiprocessing example in the python-list:
+# https://mail.python.org/pipermail/python-list/2009-February/538048.html
+
+# BEGIN SPINNER_ASYNCIO
+import asyncio
+import itertools
+import sys
+
+
+@asyncio.coroutine  # <1>
+def spin(msg):  # <2>
+    write, flush = sys.stdout.write, sys.stdout.flush
+    for char in itertools.cycle('|/-\\'):
+        status = char + ' ' + msg
+        write(status)
+        flush()
+        write('\x08' * len(status))
+        try:
+            yield from asyncio.sleep(.1)  # <3>
+        except asyncio.CancelledError:  # <4>
+            break
+    write(' ' * len(status) + '\x08' * len(status))
+
+
+@asyncio.coroutine
+def slow_function():  # <5>
+    # pretend waiting a long time for I/O
+    yield from asyncio.sleep(3)  # <6>
+    return 42
+
+
+@asyncio.coroutine
+def supervisor():  # <7>
+    spinner = asyncio.async(spin('thinking!'))  # <8>
+    print('spinner object:', spinner)  # <9>
+    result = yield from slow_function()  # <10>
+    spinner.cancel()  # <11>
+    return result
+
+
+def main():
+    loop = asyncio.get_event_loop()  # <12>
+    result = loop.run_until_complete(supervisor())  # <13>
+    loop.close()
+    print('Answer:', result)
+
+
+if __name__ == '__main__':
+    main()
+# END SPINNER_ASYNCIO