[Numpy-discussion] NEP 32: Remove the financial functions from NumPy
Sebastian Berg
sebastian at sipsolutions.net
Tue Sep 3 12:35:45 EDT 2019
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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> NumPy-Discussion at python.org
> https://mail.python.org/mailman/listinfo/numpy-discussion
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