"error: Unable to find vcvarsall.bat" when compiling Cython code

I spent hours on this, and the information was not easily findable in error: Unable to find vcvarsall.bat, that's why I post it here with the "answer your own question" feature:

• Step 1: Install Microsoft Visual C++ Compiler for Python 2.7

• Remark: You don't need to modify msvc9compiler.py as often suggested in many forum posts

• Step 2: Just add import setuptools that will help Python and "Microsoft Visual C++ Compiler for Python 2.7" work together.

  import setuptools  # important
  from distutils.core import setup
  from Cython.Build import cythonize
  setup(ext_modules=cythonize("module1.pyx", build_dir="build"),
                                             script_args=['build'], 
                                             options={'build':{'build_lib':'.'}})
  

  Note: the script_args parameter allows to run this setup.py with just python setup.py (i.e. CTRL+B in your favorite editor like Sublime Text) instead of having to pass command-line arguments like this: python setup.py build.

It works!

Python >= 3.5

I wanted to comment on @Basj (https://stackoverflow.com/a/53172602/6596203) answer but I couldn't so I apologize. I just want to add to @Basj answer for people using Python >= 3.5, instead of Microsoft Visual C++ Compiler for Python 2.7, you can install just the C++ in this installer Build Tool for Visual Studio 2019 or you can simply install that with Chocolatey.

The solution that fixed it for me. Use Anaconda and use the following:

SET DISTUTILS_USE_SDK=1 & "C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" x64

https://learn.microsoft.com/en-us/answers/questions/419525/microsoft-visual-c-140-or-greater-is-required.html

The below is said to work theoretically but didn't work for me as I encountered similar issues

The same reason this issue is present these days is because Microsoft made it. Likely a pathing issue and issue is reappearing which is Microsoft specialty since 2018.

https://github.com/pypa/setuptools/issues/3329

This might fix for you but again this is Microsoft:

import setuptools  # as requested
import distutils._msvccompiler

You can also change/check regedit:

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\VisualStudio\14.2\Setup\VC]
"ProductDir"="C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Auxiliary\\Build"

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\VisualStudio\14.0\Setup\VC]
"ProductDir"="C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Auxiliary\\Build"

Another option is to check the correct environment variables as well as delete any and all visual Studio stuff you do not need/use.

environment variable path and delete old ones and restart pc afterwards:

    C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64_arm
    C:\Users\AAAAA\AppData\Local\Programs\Microsoft VS Code\bin
    C:\Program Files (x86)\Windows Kits\10\bin\10.0.22621.0\x64