Hey there! Let's figure out why your installed Python 3.9 isn't being recognized even after running those Homebrew commands. This is a common issue caused by PATH environment variable priority—here's how to fix it:

Step 1: Identify the Current Python Path #

First, check where your python3 command is pointing right now:

which python3

If this returns /usr/bin/python3, that's Apple's pre-installed Python 3.6, which is why you're seeing that version instead of Homebrew's 3.9.

Next, find where Homebrew installed Python 3.9:

brew --prefix python@3.9

• For Intel Macs, this will likely be /usr/local/opt/python@3.9
• For Apple Silicon (M1/M2) Macs, it'll be /opt/homebrew/opt/python@3.9

The actual executable lives in the bin subfolder of that path (e.g., /usr/local/bin/python3 or /opt/homebrew/bin/python3).

Step 2: Adjust Your PATH Environment Variable #

The problem is that your system is checking /usr/bin (where Apple's Python lives) before Homebrew's bin directory. We need to flip that order.

Edit Your Shell Configuration File #

Depending on which shell you use:

• If you're using Zsh (default on macOS Catalina and later), edit ~/.zshrc
• If you're using Bash, edit ~/.bash_profile or ~/.bashrc

Open the file with a text editor (e.g., nano ~/.zshrc), and add this line at the top:

# For Intel Macs
export PATH="/usr/local/bin:$PATH"

# For Apple Silicon Macs
# export PATH="/opt/homebrew/bin:$PATH"

Uncomment the line that matches your Mac type, then save and exit (for nano: Ctrl+O, Enter, Ctrl+X).

Apply the Changes #

Reload your shell configuration to make the changes take effect immediately:

# For Zsh
source ~/.zshrc

# For Bash
source ~/.bash_profile

Step 3: Verify the Fix #

Now check again which Python is being used:

which python3

It should now point to Homebrew's bin directory (e.g., /usr/local/bin/python3). Then confirm the version:

python3 -V

You should see Python 3.9.x displayed!

Bonus Check: If You Use pyenv (Optional) #

If you have pyenv installed for Python version management, it might be overriding your Homebrew setup. In that case, you can switch to the Homebrew-installed version with:

pyenv global 3.9.1

Give these steps a try—this should resolve the version mismatch issue!

内容的提问来源于stack exchange，提问作者John