DEP: remove deprecated `numpy.dual` module

It has been deprecated since numpy 1.20, and code search engines
don't turn up a reason to keep this around.

[skip actions] [skip cirrus]

5 files changed, 1 insertions, 135 deletions

diff --git a/doc/release/upcoming_changes/23480.expired.rst b/doc/release/upcoming_changes/23480.expired.rst
new file mode 100644
index 000000000..164677b98
--- /dev/null
+++ b/doc/release/upcoming_changes/23480.expired.rst
@@ -0,0 +1 @@
+* The ``np.dual`` submodule has been removed.
diff --git a/doc/source/reference/routines.dual.rst b/doc/source/reference/routines.dual.rst
deleted file mode 100644
index 18c7791d0..000000000
--- a/doc/source/reference/routines.dual.rst
+++ /dev/null
@@ -1,47 +0,0 @@
-Optionally SciPy-accelerated routines (:mod:`numpy.dual`)
-=========================================================
-
-.. automodule:: numpy.dual
-
-Linear algebra
---------------
-
-.. currentmodule:: numpy.linalg
-
-.. autosummary::
-
-   cholesky
-   det
-   eig
-   eigh
-   eigvals
-   eigvalsh
-   inv
-   lstsq
-   norm
-   pinv
-   solve
-   svd
-
-FFT
----
-
-.. currentmodule:: numpy.fft
-
-.. autosummary::
-
-   fft
-   fft2
-   fftn
-   ifft
-   ifft2
-   ifftn
-
-Other
------
-
-.. currentmodule:: numpy
-
-.. autosummary::
-
-   i0
diff --git a/doc/source/reference/routines.rst b/doc/source/reference/routines.rst
index 24117895b..72ed80972 100644
--- a/doc/source/reference/routines.rst
+++ b/doc/source/reference/routines.rst
@@ -24,7 +24,6 @@ indentation.
    routines.ctypeslib
    routines.datetime
    routines.dtype
-   routines.dual
    routines.emath
    routines.err
    routines.fft
diff --git a/numpy/__init__.py b/numpy/__init__.py
index e41f7eae6..1880ceace 100644
--- a/numpy/__init__.py
+++ b/numpy/__init__.py
@@ -74,10 +74,6 @@ test
     Run numpy unittests
 show_config
     Show numpy build configuration
-dual
-    Overwrite certain functions with high-performance SciPy tools.
-    Note: `numpy.dual` is deprecated.  Use the functions from NumPy or Scipy
-    directly instead of importing them from `numpy.dual`.
 matlib
     Make everything matrices.
 __version__
diff --git a/numpy/dual.py b/numpy/dual.py
deleted file mode 100644
index eb7e61aac..000000000
--- a/numpy/dual.py
+++ /dev/null
@@ -1,83 +0,0 @@
-"""
-.. deprecated:: 1.20
-
-*This module is deprecated.  Instead of importing functions from*
-``numpy.dual``, *the functions should be imported directly from NumPy
-or SciPy*.
-
-Aliases for functions which may be accelerated by SciPy.
-
-SciPy_ can be built to use accelerated or otherwise improved libraries
-for FFTs, linear algebra, and special functions. This module allows
-developers to transparently support these accelerated functions when
-SciPy is available but still support users who have only installed
-NumPy.
-
-.. _SciPy : https://www.scipy.org
-
-"""
-import warnings
-
-
-warnings.warn('The module numpy.dual is deprecated.  Instead of using dual, '
-              'use the functions directly from numpy or scipy.',
-              category=DeprecationWarning,
-              stacklevel=2)
-
-# This module should be used for functions both in numpy and scipy if
-#  you want to use the numpy version if available but the scipy version
-#  otherwise.
-#  Usage  --- from numpy.dual import fft, inv
-
-__all__ = ['fft', 'ifft', 'fftn', 'ifftn', 'fft2', 'ifft2',
-           'norm', 'inv', 'svd', 'solve', 'det', 'eig', 'eigvals',
-           'eigh', 'eigvalsh', 'lstsq', 'pinv', 'cholesky', 'i0']
-
-import numpy.linalg as linpkg
-import numpy.fft as fftpkg
-from numpy.lib import i0
-import sys
-
-
-fft = fftpkg.fft
-ifft = fftpkg.ifft
-fftn = fftpkg.fftn
-ifftn = fftpkg.ifftn
-fft2 = fftpkg.fft2
-ifft2 = fftpkg.ifft2
-
-norm = linpkg.norm
-inv = linpkg.inv
-svd = linpkg.svd
-solve = linpkg.solve
-det = linpkg.det
-eig = linpkg.eig
-eigvals = linpkg.eigvals
-eigh = linpkg.eigh
-eigvalsh = linpkg.eigvalsh
-lstsq = linpkg.lstsq
-pinv = linpkg.pinv
-cholesky = linpkg.cholesky
-
-_restore_dict = {}
-
-def register_func(name, func):
-    if name not in __all__:
-        raise ValueError("{} not a dual function.".format(name))
-    f = sys._getframe(0).f_globals
-    _restore_dict[name] = f[name]
-    f[name] = func
-
-def restore_func(name):
-    if name not in __all__:
-        raise ValueError("{} not a dual function.".format(name))
-    try:
-        val = _restore_dict[name]
-    except KeyError:
-        return
-    else:
-        sys._getframe(0).f_globals[name] = val
-
-def restore_all():
-    for name in _restore_dict.keys():
-        restore_func(name)