Installing scikit-image fails to install scipy, even though it requires it

[cowlinator]

Description

Installing scikit-image 0.16.2 does not install scipy, even though it requires scipy.

Way to reproduce

"C:\Program Files\Python39\python.exe" -m venv venv39_temp1
venv39_temp1\Scripts\activate
python -m pip install --upgrade pip setuptools wheel
python -m pip install scikit-image==0.16.2
python -c "from skimage.metrics import structural_similarity"

Output from reproduction steps

D:\Dev\1>"C:\Program Files\Python39\python.exe" -m venv venv39_temp1

D:\Dev\1>venv39_temp1\Scripts\activate

(venv39_temp1) D:\Dev\1> python -m pip install --upgrade pip setuptools wheel
Collecting pip
  Using cached pip-21.1.1-py3-none-any.whl (1.5 MB)
Collecting setuptools
  Using cached setuptools-56.2.0-py3-none-any.whl (785 kB)
Collecting wheel
  Using cached wheel-0.36.2-py2.py3-none-any.whl (35 kB)
Installing collected packages: pip, setuptools, wheel
  Attempting uninstall: pip
    Found existing installation: pip 20.2.3
    Uninstalling pip-20.2.3:
      Successfully uninstalled pip-20.2.3
  Attempting uninstall: setuptools
    Found existing installation: setuptools 49.2.1
    Uninstalling setuptools-49.2.1:
      Successfully uninstalled setuptools-49.2.1
Successfully installed pip-21.1.1 setuptools-56.2.0 wheel-0.36.

(venv39_temp1) D:\Dev\1>python -m pip install scikit-image==0.16.2
Collecting scikit-image==0.16.2
  Using cached scikit_image-0.16.2-cp39-cp39-win_amd64.whl
Collecting imageio>=2.3.0
  Using cached imageio-2.9.0-py3-none-any.whl (3.3 MB)
Collecting pillow>=4.3.0
  Using cached Pillow-8.2.0-cp39-cp39-win_amd64.whl (2.2 MB)
Collecting PyWavelets>=0.4.0
  Using cached PyWavelets-1.1.1-cp39-cp39-win_amd64.whl (4.2 MB)
Collecting networkx>=2.0
  Using cached networkx-2.5.1-py3-none-any.whl (1.6 MB)
Collecting numpy
  Using cached numpy-1.20.3-cp39-cp39-win_amd64.whl (13.7 MB)
Collecting decorator<5,>=4.3
  Using cached decorator-4.4.2-py2.py3-none-any.whl (9.2 kB)
Installing collected packages: pillow, numpy, decorator, PyWavelets, networkx, imageio, scikit-image
Successfully installed PyWavelets-1.1.1 decorator-4.4.2 imageio-2.9.0 networkx-2.5.1 numpy-1.20.3 pillow-8.2.0 scikit-image-0.16.2

(venv39_temp1) D:\Dev\1>python -c "from skimage.metrics import structural_similarity"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "D:\Dev\1\venv39_temp1\lib\site-packages\skimage\metrics\__init__.py", line 1, in <module>
    from ._adapted_rand_error import adapted_rand_error
  File "D:\Dev\1\venv39_temp1\lib\site-packages\skimage\metrics\_adapted_rand_error.py", line 2, in <module>
    from ._contingency_table import contingency_table
  File "D:\Dev\1\venv39_temp1\lib\site-packages\skimage\metrics\_contingency_table.py", line 1, in <module>
    import scipy.sparse as sparse
ModuleNotFoundError: No module named 'scipy'

Version information

# Paste the output of the following python commands
from __future__ import print_function
import sys; print(sys.version)
import platform; print(platform.platform())
import skimage; print("scikit-image version: {}".format(skimage.__version__))
import numpy; print("numpy version: {}".format(numpy.__version__))

3.9.4 (tags/v3.9.4:1f2e308, Apr  6 2021, 13:40:21) [MSC v.1928 64 bit (AMD64)]
Windows-10-10.0.18362-SP0
scikit-image version: 0.16.2
numpy version: 1.20.3

Why am I using version 0.16.2 ?

As a workaround to this issue in version 0.18: #4780 (comment)

[hmaarrfk]

Unfortunately, scikit-image 0.16.2 is neither currently supported, nor was it ever supported for installation on Python 3.9.

Is there a particular reason you need scikit-image 0.16.2 instead of updating to the latest version?

[cowlinator]

Why am I using version 0.16.2 ?

As a workaround to this issue in version 0.18: #4780 (comment)

[cowlinator]

@hmaarrfk , also, where is it documented which versions of scikit-image support which versions of Python?

Setup.py lists in 2 places that 0.16.2 has forward-compatibility for all versions of python greater than 3.6.

https://github.com/scikit-image/scikit-image/blob/v0.16.2/setup.py#L41

https://github.com/scikit-image/scikit-image/blob/v0.16.2/setup.py#L233

[hmaarrfk]

we should probably be more explicit.

it is "greater than 3.6 [at the time of writing]".

I typically check for compatibility by looking at the files available on pypi

They should be avaiable for your version of python
https://pypi.org/project/scikit-image/#files

[mkcor]

Dear @cowlinator,

Were you able to resolve your install issue?

[grlee77]

moving from discussion back to issues, but leaving closed due to lack of feedback