:py3 command does not work in macvim launching from dock

Describe the bug
:py3 command works correctly in mvim which launches from terminal, but does not work in mvim launching from dock.

To Reproduce
Detailed steps to reproduce the behavior:

1. launch macvim from dock
2. :py3 import subprocess
3. :py3 print( subprocess.Popen('rg ""', shell=True, stdout=subprocess.PIPE).stdout.read() )
4. show nothing

Expected behavior

1. launch macvim from terminal
2. :py3 import subprocess
3. :py3 print( subprocess.Popen('rg ""', shell=True, stdout=subprocess.PIPE).stdout.read() )
4. show the rg output lines

Screenshots
The wrong one:

The correct one:

Environment (please complete the following information):
Vim version:

• OS: [e.g. Ubuntu 18.04, Windows 10 1809, macOS 10.14]
  

Additional context
I installed macvim by brew cask install macvim

首先比较从 Dock 启动 MacVim 与从终端启动 MacVim 时 :py3 subprocess 调用可用的环境，并使用报告中的 rg 命令作为复现程序。当从 Dock 启动的应用产生与从终端启动的应用相同的 rg 输出时，确认完成。