Check maximum Python version in mach (servo#34490)

Mach is currently failing bootstrap and building if the Python version
is greater than 3.12. This is because wpt does not support 3.13 yet.
This causes confusion for people running recent distros that ship 3.13
by default.

I changed the logic so that mach checks both the minimum and the maximum
supported versions of Python instead of just checking the minimum. It
will now also tell you which maximum version is supported.

I also updated the README.md to specify the supported Python versions
so that people don't accidentally install the wrong version.

Signed-off-by: Michael Mc Donnell <[email protected]>

README.md

@@ -17,15 +17,15 @@ For more detailed build instructions, see the Servo book under [Setting up your
 
 ### macOS
 
-- Download and install [`python`](https://www.python.org/downloads/macos/), [Xcode](https://developer.apple.com/xcode/), and [`brew`](https://brew.sh/)
+- Download and install [`python`](https://www.python.org/downloads/macos/) (version 3.10 to 3.12), [Xcode](https://developer.apple.com/xcode/), and [`brew`](https://brew.sh/).
 - Install `rustup`: `curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh`
 - Restart your shell to make sure `cargo` is available
 - Install the other dependencies: `./mach bootstrap`
 - Build servoshell: `./mach build`
 
 ### Linux
 
-- Install `curl` and `python`:
+- Install `curl` and `python` (version 3.10 to 3.12):
   - Arch: `sudo pacman -S --needed curl python python-pip`
   - Debian, Ubuntu: `sudo apt install curl python3-pip python3-venv python3-setuptools`
   - Fedora: `sudo dnf install curl python3 python3-pip python3-devel`
@@ -37,7 +37,7 @@ For more detailed build instructions, see the Servo book under [Setting up your
 
 ### Windows
 
-- Download and install [`python`](https://www.python.org/downloads/windows/), [`choco`](https://chocolatey.org/install#individual), and [`rustup`](https://win.rustup.rs/)
+- Download and install [`python`](https://www.python.org/downloads/windows/) (version 3.10 to 3.12), [`choco`](https://chocolatey.org/install#individual), and [`rustup`](https://win.rustup.rs/)
   - Be sure to select *Quick install via the Visual Studio Community installer*
 - In the Visual Studio Installer, ensure the following components are installed:
   - **Windows 10 SDK (10.0.19041.0)** (`Microsoft.VisualStudio.Component.Windows10SDK.19041`)

mach

@@ -12,11 +12,15 @@
 import os
 import sys
 
-if sys.version_info < (3, 10):
-    print("mach does not support python < 3.10, please install python 3 >= 3.10")
+# Destructure because version_info > max_ver is true when running the same version.
+ver = (sys.version_info[0], sys.version_info[1])
+min_ver = (3, 10)
+max_ver = (3, 12) # WPT does not support Python 3.13. See issue #34095.
+if ver < min_ver or ver > max_ver:
+    print("mach does not support python {0}.{1}, please install 3.{2} <= python <= 3.{3}" \
+        .format(ver[0], ver[1], min_ver[1], max_ver[1]))
     sys.exit(1)
 
-
 def main(args):
     topdir = os.path.abspath(os.path.dirname(sys.argv[0]))
     sys.path.insert(0, os.path.join(topdir, "python"))