Python

When you will meet it

Step one of installing an AI tool is usually 'check you have Python'; step two is 'pip install something' — and both fail often. If you do not recognise the python3 command, or do not know your machine holds several Pythons at once, you get stuck in environment setup and blame the AI tool.

Minimal example

python3 --version        # 看版本（Windows 通常要寫 python --version）
which -a python3         # macOS / Linux：列出電腦上「所有」的 python3
where.exe python         # Windows：同上

which -a often prints two or three paths: the system one, the Homebrew one, one you installed yourself. The python3 you type uses only the first in that list — and most later environment problems trace straight back to it.

What people get wrong

• Assuming you must learn to write Python before you can use AI tools. You need only three things: run it, install packages into it, and read its error messages.
• Assuming there is one Python on your machine. macOS ships one, Homebrew adds one, the python.org installer adds another. Installing into A and running B produces 'I installed it but it says not found'.