Mailman 3 Re: [Numpy-discussion] round / set_printoptions discrepancy - NumPy-Discussion

13 Sep 2019


      In my opinion the problem is that numpy floats break the Liskov substitution principle,
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pyfloat = 16.055
npfloat = np.float64(pyfloat)
isinstance(npfloat, float)
True
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round(pyfloat, 2)
16.05
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round(npfloat, 2)
16.06
Since numpy.float64 is a subclass of builtins.float I would expect that
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round(x, j) == round(np.float64(x), j)
is an invariant, but unfortunately this is not the case.
Moreover the python3 semantics of the round function require that when the number of digits is None,
the return value should be of integral type:
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round(pyfloat)
16
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round(pyfloat, None)
16
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round(pyfloat, 0)
16.0
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round(npfloat)
16.0
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round(npfloat, None)
16.0
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round(npfloat, 0)
16.0
see also https://github.com/numpy/numpy/issues/11810
Stefano

Re: [Numpy-discussion] round / set_printoptions discrepancy

Stefano Miccoli

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