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For instance, multiprocessing behaves like this:
>>> multiprocessing.Pool(-1)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "C:\Python34\lib\multiprocessing\context.py", line 118, in Pool
 context=self.get_context())
 File "C:\Python34\lib\multiprocessing\pool.py", line 157, in __init__
 raise ValueError("Number of processes must be at least 1")
ValueError: Number of processes must be at least 1
>>>