Incorect Python version on MacOS latest

[NicolasGensollen]

Describe the bug

On MacOS-latest, the version of Python is not the expected one.
The following input:

name: 'test'                                                                                                                                                                                               
                                                                                                                                                                                                            
 on:                                                                                                                                                                                                        
   push:                                                                                                                                                                                                    
     branches:                                                                                                                                                                                              
       - "main"                                                                                                                                                                                             
   pull_request:                                                                                                                                                                                            
     branches:                                                                                                                                                                                              
       - '*'                                                                                                                                                                                                
                                                                                                                                                                                                            
 jobs:                                                                                                                                                                                                      
   build:                                                                                                                                                                                                   
     runs-on: ${{ matrix.os }}                                                                                                                                                                              
     strategy:                                                                                                                                                                                              
       matrix:                                                                                                                                                                                              
         os: [ubuntu-latest, windows-latest, macos-latest]                                                                                                                                                  
         python-version: ["3.7"]                                                                                                                                                                            
     steps:                                                                                                                                                                                                 
       - uses: actions/checkout@v2                                                                                                                                                                          
       - name: Set up Python                                                                                                                                                                                
         uses: actions/setup-python@v2                                                                                                                                                                      
         with:                                                                                                                                                                                              
           python-version: ${{ matrix.python-version }}                                                                                                                                                     
       - shell: bash -l {0}                                                                                                                                                                                 
         name: 'Display Python version and location'                                                                                                                                                        
         run: |                                                                                                                                                                                             
             python --version                                                                                                                                                                               
             which python

yields the following output:

Ubuntu

Python 3.7.9
/opt/hostedtoolcache/Python/3.7.9/x64/bin/python

Windows

Python 3.7.9
/c/hostedtoolcache/windows/Python/3.7.9/x64/python

MacOS

Python 2.7.18
/usr/local/bin/python

Which version of the action are you using?

• v1
• v2
• Some other tag (such as v2.0.1 or master)

Environment

• self-hosted
• Linux
• Windows
• Mac

Am I missing something here?
Thanks!

[yuxiang-he]

Also adding on to the issue here, all dependencies in our tests were installed in /Library/Frameworks/Python.framework/Versions/2.7/bin which is not on $PATH of the test environment by default.

[maxim-lobanov]

Hello,
Your issue is caused by -l argument in - shell: bash -l {0}.

actions/setup-python prepends $PATH with folder where specified Python is located. But when you add -l argument, bash is run in login mode and bash itself prepends $PATH with a few more folders including /usr/local/bin that contains default Python on MacOS.
I can confirm that same behavior on my local macOS machine. If bash is run like bash -l, it contains additional folders to PATH and there is no way to avoid it.

I have done a few experiments:

   runs-on: macos-latest
   steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2
       with:
         python-version: 3.7
     - run: |
         echo $PATH
         python --version
         which python
     - run: |
         echo $PATH
         python --version
         which python
       shell: bash {0}
     - run: |
         echo $PATH
         python --version
         which python
       shell: bash -l {0}

The first bash step output (specified Python is the first in PATH):

/Users/runner/hostedtoolcache/Python/3.7.9/x64/bin:/Users/runner/hostedtoolcache/Python/3.7.9/x64:/usr/local/opt/pipx_bin:/Users/runner/.cargo/bin:/usr/local/lib/ruby/gems/2.7.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/curl/bin:/usr/local/bin:/usr/local/sbin:/Users/runner/bin:/Users/runner/.yarn/bin:/usr/local/go/bin:/Users/runner/Library/Android/sdk/tools:/Users/runner/Library/Android/sdk/platform-tools:/Users/runner/Library/Android/sdk/ndk-bundle:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/usr/bin:/bin:/usr/sbin:/sbin:/Users/runner/.dotnet/tools:/Users/runner/.ghcup/bin:/Users/runner/hostedtoolcache/stack/2.5.1/x64
Python 3.7.9
/Users/runner/hostedtoolcache/Python/3.7.9/x64/bin/python

The second bash step output (specified Python is the first in PATH):

/Users/runner/hostedtoolcache/Python/3.7.9/x64/bin:/Users/runner/hostedtoolcache/Python/3.7.9/x64:/usr/local/opt/pipx_bin:/Users/runner/.cargo/bin:/usr/local/lib/ruby/gems/2.7.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/curl/bin:/usr/local/bin:/usr/local/sbin:/Users/runner/bin:/Users/runner/.yarn/bin:/usr/local/go/bin:/Users/runner/Library/Android/sdk/tools:/Users/runner/Library/Android/sdk/platform-tools:/Users/runner/Library/Android/sdk/ndk-bundle:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/usr/bin:/bin:/usr/sbin:/sbin:/Users/runner/.dotnet/tools:/Users/runner/.ghcup/bin:/Users/runner/hostedtoolcache/stack/2.5.1/x64
Python 3.7.9
/Users/runner/hostedtoolcache/Python/3.7.9/x64/bin/python

The third bash step output (bash is run with -l flag and bash adds additional folders to PATH):

/usr/local/opt/pipx_bin:/Users/runner/.cargo/bin:/usr/local/lib/ruby/gems/2.7.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/curl/bin:/usr/local/bin:/usr/local/sbin:/Users/runner/bin:/Users/runner/.yarn/bin:/usr/local/go/bin:/Users/runner/Library/Android/sdk/tools:/Users/runner/Library/Android/sdk/platform-tools:/Users/runner/Library/Android/sdk/ndk-bundle:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/Users/runner/hostedtoolcache/Python/3.7.9/x64/bin:/Users/runner/hostedtoolcache/Python/3.7.9/x64:/usr/local/opt/pipx_bin:/Users/runner/.cargo/bin:/usr/local/lib/ruby/gems/2.7.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/curl/bin:/usr/local/sbin:/Users/runner/bin:/Users/runner/.yarn/bin:/usr/local/go/bin:/Users/runner/Library/Android/sdk/tools:/Users/runner/Library/Android/sdk/platform-tools:/Users/runner/Library/Android/sdk/ndk-bundle:/Users/runner/.dotnet/tools:/Users/runner/.ghcup/bin:/Users/runner/hostedtoolcache/stack/2.5.1/x64:/Users/runner/.dotnet/tools:/Users/runner/.ghcup/bin:/Users/runner/hostedtoolcache/stack/2.5.1/x64
Python 2.7.18
/usr/local/bin/python

Unfortunately, there is no way to fix it from task side since it is by design.
I suggest using shell without -l argument or adds the following line to bash step to prepend PATH already after bash initialization:

export PATH="$pythonLocation:$PATH"

[NicolasGensollen]

Thanks for the explanations @maxim-lobanov !
I confirm that the proposed solutions work for me, closing this...