Opencv-python: Installation takes so much time

[ghimireadarsh]

System information (version)

• OpenCV => 4.4
• Operating System / Platform => Mac OSX 64 bit, OSX version 10.12.6
• Environment => virtualenv
• Python => 3.7.6

Detailed description

It takes more than 30 minutes to install, and is stuck at installation for more than 30 minutes.

Building wheel for opencv-python (PEP 517) ...

Steps to reproduce

pip install opencv-python

Issue submission checklist

• [x] I report the issue, it's not a question
  
• [x] I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
  

[skvark]

Yeah, building from source takes time. It's normal for heavy C++ projects such as OpenCV. And if you are wondering why that happens: there are no pre-built wheels for macOS 10.12. Pre-built wheels are provided only for 10.13 and later: https://github.com/skvark/opencv-python#backward-compatibility

Solutions: upgrade your OS or just wait for the compilation to finish.

[abhiTronix]

@skvark Headsup, now opencv-python only provides pre-built wheels for 10.15 and later with commit: 6336ca866644dc5daf64831a4352c23479e1d248 that pins macos-latest or macos-10.15 for building these binaries. See:
https://github.com/opencv/opencv-python/blob/86c3d2a285c16f95a66c07275187da3f95be0af5/.github/workflows/build_wheels_macos.yml#L24-L30

[abhiTronix]

@asmorkalov please reflect this update in README too.