renumbering chapters >= 19

19-concurrency/spinner_proc.py

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+# spinner_proc.py
+
+# credits: Adapted from Michele Simionato's
+# multiprocessing example in the python-list:
+# https://mail.python.org/pipermail/python-list/2009-February/675659.html
+
+# tag::SPINNER_PROC_IMPORTS[]
+import itertools
+import time
+from multiprocessing import Process, Event  # <1>
+from multiprocessing import synchronize     # <2>
+
+def spin(msg: str, done: synchronize.Event) -> None:  # <3>
+# end::SPINNER_PROC_IMPORTS[]
+    for char in itertools.cycle(r'\|/-'):
+        status = f'\r{char} {msg}'
+        print(status, end='', flush=True)
+        if done.wait(.1):
+            break
+    blanks = ' ' * len(status)
+    print(f'\r{blanks}\r', end='')
+
+def slow() -> int:
+    time.sleep(3)
+    return 42
+
+# tag::SPINNER_PROC_SUPER[]
+def supervisor() -> int:
+    done = Event()
+    spinner = Process(target=spin,               # <4>
+                      args=('thinking!', done))
+    print(f'spinner object: {spinner}')          # <5>
+    spinner.start()
+    result = slow()
+    done.set()
+    spinner.join()
+    return result
+# end::SPINNER_PROC_SUPER[]
+
+def main() -> None:
+    result = supervisor()
+    print(f'Answer: {result}')
+
+
+if __name__ == '__main__':
+    main()
+