[Numpy-discussion] NEP 32: Remove the financial functions from NumPy

Ilhan Polat ilhanpolat at gmail.com
Wed Sep 4 14:10:11 EDT 2019


+1 on removing them from NumPy. I think there are plenty of alternatives
already so many that we might even consider deprecating them just like
SciPy misc module by pointing to alternatives.

On Tue, Sep 3, 2019 at 6:38 PM Sebastian Berg <sebastian at sipsolutions.net>
wrote:

> On Tue, 2019-09-03 at 08:56 -0400, Warren Weckesser wrote:
> > Github issue 2880 ("Get financial functions out of main namespace",
>
> Very briefly, I am absolutely in favor of this.
>
> Keeping the functions in numpy seems more of a liability than help
> anyone. And this push is more likely to help users by spurring
> development on a good replacement, than a practically unmaintained
> corner of NumPy that may seem like it solves a problem, but probably
> does so very poorly.
>
> Moving them into a separate pip installable package seems like the best
> way forward until a better replacement, to which we can point users,
> comes up.
>
> - Sebastian
>
>
> > https://github.com/numpy/numpy/issues/2880) has been open since 2013.
> > In a recent community meeting, it was suggested that we create a NEP
> > to propose the removal of the financial functions from NumPy.  I have
> > submitted "NEP 32:  Remove the financial functions from NumPy" in a
> > pull request at https://github.com/numpy/numpy/pull/14399.  A copy of
> > the latest version of the NEP is below.
> >
> > According to the NEP process document, "Once the PR is in place, the
> > NEP should be announced on the mailing list for discussion (comments
> > on the PR itself should be restricted to minor editorial and
> > technical fixes)."  This email is the announcement for NEP 32.
> >
> > The NEP includes a brief summary of the history of the financial
> > functions, and has links to several relevant mailing list threads,
> > dating back to when the functions were added to NumPy in 2008.  I
> > recommend reviewing those threads before commenting here.
> >
> > Warren
> >
> > -----
> >
> > ==================================================
> > NEP 32 — Remove the financial functions from NumPy
> > ==================================================
> >
> > :Author: Warren Weckesser <warren.weckesser at gmail.com>
> > :Status: Draft
> > :Type: Standards Track
> > :Created: 2019-08-30
> >
> >
> > Abstract
> > --------
> >
> > We propose deprecating and ultimately removing the financial
> > functions [1]_
> > from NumPy.  The functions will be moved to an independent
> > repository,
> > and provided to the community as a separate package with the name
> > ``numpy_financial``.
> >
> >
> > Motivation and scope
> > --------------------
> >
> > The NumPy financial functions [1]_ are the 10 functions ``fv``,
> > ``ipmt``,
> > ``irr``, ``mirr``, ``nper``, ``npv``, ``pmt``, ``ppmt``, ``pv`` and
> > ``rate``.
> > The functions provide elementary financial calculations such as
> > future value,
> > net present value, etc. These functions were added to NumPy in 2008
> > [2]_.
> >
> > In May, 2009, a request by Joe Harrington to add a function called
> > ``xirr`` to
> > the financial functions triggered a long thread about these functions
> > [3]_.
> > One important point that came up in that thread is that a "real"
> > financial
> > library must be able to handle real dates.  The NumPy financial
> > functions do
> > not work with actual dates or calendars.  The preference for a more
> > capable
> > library independent of NumPy was expressed several times in that
> > thread.
> >
> > In June, 2009, D. L. Goldsmith expressed concerns about the
> > correctness of the
> > implementations of some of the financial functions [4]_.  It was
> > suggested then
> > to move the financial functions out of NumPy to an independent
> > package.
> >
> > In a GitHub issue in 2013 [5]_, Nathaniel Smith suggested moving the
> > financial
> > functions from the top-level namespace to ``numpy.financial``.  He
> > also
> > suggested giving the functions better names.  Responses at that time
> > included
> > the suggestion to deprecate them and move them from NumPy to a
> > separate
> > package.  This issue is still open.
> >
> > Later in 2013 [6]_, it was suggested on the mailing list that these
> > functions
> > be removed from NumPy.
> >
> > The arguments for the removal of these functions from NumPy:
> >
> > * They are too specialized for NumPy.
> > * They are not actually useful for "real world" financial
> > calculations, because
> >   they do not handle real dates and calendars.
> > * The definition of "correctness" for some of these functions seems
> > to be a
> >   matter of convention, and the current NumPy developers do not have
> > the
> >   background to judge their correctness.
> > * There has been little interest among past and present NumPy
> > developers
> >   in maintaining these functions.
> >
> > The main arguments for keeping the functions in NumPy are:
> >
> > * Removing these functions will be disruptive for some users.
> > Current users
> >   will have to add the new ``numpy_financial`` package to their
> > dependencies,
> >   and then modify their code to use the new package.
> > * The functions provided, while not "industrial strength", are
> > apparently
> >   similar to functions provided by spreadsheets and some
> > calculators.  Having
> >   them available in NumPy makes it easier for some developers to
> > migrate their
> >   software to Python and NumPy.
> >
> > It is clear from comments in the mailing list discussions and in the
> > GitHub
> > issues that many current NumPy developers believe the benefits of
> > removing
> > the functions outweigh the costs.  For example, from [5]_::
> >
> >     The financial functions should probably be part of a separate
> > package
> >     -- Charles Harris
> >
> >     If there's a better package we can point people to we could just
> > deprecate
> >     them and then remove them entirely... I'd be fine with that
> > too...
> >     -- Nathaniel Smith
> >
> >     +1 to deprecate them. If no other package exists, it can be
> > created if
> >     someone feels the need for that.
> >     -- Ralf Gommers
> >
> >     I feel pretty strongly that we should deprecate these. If nobody
> > on numpy’s
> >     core team is interested in maintaining them, then it is purely a
> > drag on
> >     development for NumPy.
> >     -- Stephan Hoyer
> >
> > And from the 2013 mailing list discussion, about removing the
> > functions from
> > NumPy::
> >
> >     I am +1 as well, I don't think they should have been included in
> > the first
> >     place.
> >     -- David Cournapeau
> >
> > But not everyone was in favor of removal::
> >
> >     The fin routines are tiny and don't require much maintenance once
> >     written.  If we made an effort (putting up pages with examples of
> > common
> >     financial calculations and collecting those under a topical web
> > page,
> >     then linking to that page from various places and talking it up),
> > I
> >     would think they could attract users looking for a free way to
> > play with
> >     financial scenarios.  [...]
> >     So, I would say we keep them.  If ours are not the best, we
> > should bring
> >     them up to snuff.
> >     -- Joe Harrington
> >
> > For an idea of the maintenance burden of the financial functions, one
> > can
> > look for all the GitHub issues [7]_ and pull requests [8]_ that have
> > the tag
> > ``component: numpy.lib.financial``.
> >
> > One method for measuring the effect of removing these functions is to
> > find
> > all the packages on GitHub that use them.  Such a search can be
> > performed
> > with the ``python-api-inspect`` service [9]_.  A search for all uses
> > of the
> > NumPy financial functions finds just eight repositories.  (See the
> > comments
> > in [5]_ for the actual SQL query.)
> >
> >
> > Implementation
> > --------------
> >
> > * Create a new Python package, ``numpy_financial``, to be maintained
> > in the
> >   top-level NumPy github organization.  This repository will contain
> > the
> >   definitions and unit tests for the financial functions.  The
> > package will
> >   be added to PyPI so it can be installed with ``pip``.
> > * Deprecate the financial functions in the ``numpy`` namespace,
> > beginning in
> >   NumPy version 1.18. Remove the financial functions from NumPy
> > version 1.20.
> >
> >
> > Backward compatibility
> > ----------------------
> >
> > The removal of these functions breaks backward compatibility, as
> > explained
> > earlier.  The effects are mitigated by providing the
> > ``numpy_financial``
> > library.
> >
> >
> > Alternatives
> > ------------
> >
> > The following alternatives were mentioned in [5]_:
> >
> > * *Maintain the functions as they are (i.e. do nothing).*
> >   A review of the history makes clear that this is not the preference
> > of many
> >   NumPy developers.  A recurring comment is that the functions simply
> > do not
> >   belong in NumPy.  When that sentiment is combined with the history
> > of bug
> >   reports and the ongoing questions about the correctness of the
> > functions, the
> >   conclusion is that the cleanest solution is deprecation and
> > removal.
> > * *Move the functions from the ``numpy`` namespace to
> > ``numpy.financial``.*
> >   This was the initial suggestion in [5]_.  Such a change does not
> > address the
> >   maintenance issues, and doesn't change the misfit that many
> > developers see
> >   between these functions and NumPy.  It causes disruption for the
> > current
> >   users of these functions without addressing what many developers
> > see as the
> >   fundamental problem.
> >
> >
> > Discussion
> > ----------
> >
> > Links to past mailing list discussions, and to relevant GitHub issues
> > and pull
> > requests, have already been given.
> >
> >
> > References and footnotes
> > ------------------------
> >
> > .. [1] Financial functions,
> >    https://numpy.org/doc/1.17/reference/routines.financial.html
> >
> > .. [2] Numpy-discussion mailing list, "Simple financial functions for
> > NumPy",
> >
> >
> https://mail.python.org/pipermail/numpy-discussion/2008-April/032353.html
> >
> > .. [3] Numpy-discussion mailing list, "add xirr to numpy financial
> > functions?",
> >
> > https://mail.python.org/pipermail/numpy-discussion/2009-May/042645.html
> >
> > .. [4] Numpy-discussion mailing list, "Definitions of pv, fv, nper,
> > pmt, and rate",
> >
> > https://mail.python.org/pipermail/numpy-discussion/2009-June/043188.html
> >
> > .. [5] Get financial functions out of main namespace,
> >    https://github.com/numpy/numpy/issues/2880
> >
> > .. [6] Numpy-discussion mailing list, "Deprecation of financial
> > routines",
> >
> >
> https://mail.python.org/pipermail/numpy-discussion/2013-August/067409.html
> >
> > .. [7] ``component: numpy.lib.financial`` issues,
> >
> >
> https://github.com/numpy/numpy/issues?utf8=%E2%9C%93&q=is%3Aissue+label%3A%22component%3A+numpy.lib.financial%22+
> >
> > .. [8] ``component: numpy.lib.financial`` pull request,
> >
> >
> https://github.com/numpy/numpy/pulls?utf8=%E2%9C%93&q=is%3Apr+label%3A%22component%3A+numpy.lib.financial%22+
> >
> > .. [9] Quansight-Labs/python-api-inspect,
> >    https://github.com/Quansight-Labs/python-api-inspect/
> >
> >
> > Copyright
> > ---------
> >
> > This document has been placed in the public domain.
> >
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