I've been using and teaching python for close to 20 years and I never noticed that x.is_integer() exists until this thread. I would say the "one obvious way" is less than obvious.
On the other hand, `x == int(x)` is genuinely obvious... and it immediately suggests the probably better `math.isclose(x, int(x))` that is what you usually mean. On Wed, Mar 21, 2018, 2:08 PM Mark Dickinson <dicki...@gmail.com> wrote: > I'd prefer to see `float.is_integer` stay. There _are_ occasions when one > wants to check that a floating-point number is integral, and on those > occasions, using `x.is_integer()` is the one obvious way to do it. I don't > think the fact that it can be misused should be grounds for deprecation. > > As far as real uses: I didn't find uses of `is_integer` in our code base > here at Enthought, but I did find plenty of places where it _could_ > reasonably have been used, and where something less readable like `x % 1 == > 0` was being used instead. For evidence that it's generally useful: it's > already been noted that the decimal module uses it internally. The mpmath > package defines its own "isint" function and uses it in several places: see > https://github.com/fredrik-johansson/mpmath/blob/2858b1000ffdd8596defb50381dcb83de2bcccc6/mpmath/ctx_mp_python.py#L764. > MPFR also has an mpfr_integer_p predicate: > http://www.mpfr.org/mpfr-current/mpfr.html#index-mpfr_005finteger_005fp. > > A concrete use-case: suppose you wanted to implement the beta function ( > https://en.wikipedia.org/wiki/Beta_function) for real arguments in > Python. You'll likely need special handling for the poles, which occur only > for some negative integer arguments, so you'll need an is_integer test for > those. For small positive integer arguments, you may well want the accuracy > advantage that arises from computing the beta function in terms of > factorials (giving a correctly-rounded result) instead of via the log of > the gamma function. So again, you'll want an is_integer test to identify > those cases. (Oddly enough, I found myself looking at this recently as a > result of the thread about quartile definitions: there are links between > the beta function, the beta distribution, and order statistics, and the > (k-1/3)/(n+1/3) expression used in the recommended quartile definition > comes from an approximation to the median of a beta distribution with > integral parameters.) > > Or, you could look at the SciPy implementation of the beta function, which > does indeed do the C equivalent of is_integer in many places: > https://github.com/scipy/scipy/blob/11509c4a98edded6c59423ac44ca1b7f28fba1fd/scipy/special/cephes/beta.c#L67 > > In sum: it's an occasionally useful operation; there's no other obvious, > readable spelling of the operation that does the right thing in all cases, > and it's _already_ in Python! In general, I'd think that deprecation of an > existing construct should not be done lightly, and should only be done when > there's an obvious and significant benefit to that deprecation. I don't see > that benefit here. > > -- > Mark > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/mertz%40gnosis.cx >
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