spanner_client = spanner.Client()

# Get an instance, but provide a non-existent instance id
instance = spanner_client.instance('non_existent_spanner_instance')

database = instance.database('real_database_id_on_different_instance')
with database.snapshot() as snapshot:
  results = snapshot.execute_sql('SELECT 1')

  for row in results:
      print(row)

 File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/cloud/spanner_v1/database.py", line 499, in __enter__
    session = self._session = self._database._pool.get()
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/cloud/spanner_v1/pool.py", line 268, in get
    session.create()
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/cloud/spanner_v1/session.py", line 116, in create
    session_pb = api.create_session(self._database.name, metadata=metadata, **kw)
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/cloud/spanner_v1/gapic/spanner_client.py", line 290, in create_session
    request, retry=retry, timeout=timeout, metadata=metadata
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/api_core/gapic_v1/method.py", line 143, in __call__
    return wrapped_func(*args, **kwargs)
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/api_core/retry.py", line 273, in retry_wrapped_func
    on_error=on_error,
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/api_core/retry.py", line 182, in retry_target
    return target()
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/api_core/timeout.py", line 214, in func_with_timeout
    return func(*args, **kwargs)
  File "/usr/local/google/home/donghuiz/.local/lib/python2.7/site-packages/google/api_core/grpc_helpers.py", line 59, in error_remapped_callable
    six.raise_from(exceptions.from_grpc_error(exc), exc)
  File "/usr/lib/python2.7/dist-packages/six.py", line 737, in raise_from
    raise value
google.api_core.exceptions.InvalidArgument: 400 Invalid CreateSession request.