title: python 3.8 shared memory example giving different values
body: <p>I am trying to use the new shared memory example in python 3.8 from this link <a href="https://docs.python.org/3/library/multiprocessing.shared_memory.html" rel="nofollow noreferrer">https://docs.python.org/3/library/multiprocessing.shared_memory.html</a> </p>
  
  <pre><code># In the first Python interactive shell
  import numpy as np
  a = np.array([1, 1, 2, 3, 5, 8])  # Start with an existing NumPy array
  from multiprocessing import shared_memory
  shm = shared_memory.SharedMemory(create=True, size=a.nbytes)
  # Now create a NumPy array backed by shared memory
  b = np.ndarray(a.shape, dtype=a.dtype, buffer=shm.buf)
  b[:] = a[:]  # Copy the original data into shared memory
  shname = shm.name  # We did not specify a name so one was chosen for us
  print(shname)
  print(a)
  print(b)
  
  # In either the same shell or a new Python shell on the same machine
  import numpy as np
  from multiprocessing import shared_memory
  # Attach to the existing shared memory block
  existing_shm = shared_memory.SharedMemory(name=shname)
  # Note that a.shape is (6,) and a.dtype is np.int64 in this example
  c = np.ndarray((6,), dtype=np.int64, buffer=existing_shm.buf)
  print(c)
  c[-1] = 888
  print(c)
  # Back in the first Python interactive shell, b reflects this change
  
  # Clean up from within the second Python shell
  del c  # Unnecessary; merely emphasizing the array is no longer used
  existing_shm.close()
  
  # Clean up from within the first Python shell
  del b  # Unnecessary; merely emphasizing the array is no longer used
  shm.close()
  shm.unlink()  # Free and release the shared memory block at the very end
  </code></pre>
  
  <p>In the example, the output of <code>c</code> should be <code>array([1, 1, 2, 3, 5, 8])</code> however when I run this I get: </p>
  
  <pre><code>wnsm_26020d1b
  [1 1 2 3 5 8]
  [1 1 2 3 5 8]
  [ 4294967297 12884901890 34359738373           0           0           0]
  [ 4294967297 12884901890 34359738373           0           0         888]
  </code></pre>
  
  <p>Did I totally miss something? Anyone else have this result?</p>