The default depends on your system. On a 64-bit system, default types will be 64-bit. On a 32-bit system, default types will be 32-bit. There is no way to change the default short of re-compiling numpy with a different system C header.
You can of course specify dtypes explicitly, e.g.
>>> x = np.array(1, dtype='int32')
Edit: as kazemakase mentions below, the above is only true for int32/int64. In recent numpy versions, the default for floating-point is float64 regardless of the system.
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