如何将Python 3设为默认应用？解决脚本无法在解释器运行问题

Hey there! Let's work through this Python 2 and 3 coexistence problem together—super common issue, so we’ve got this.

The reason your old scripts started opening in Notepad after installing Python 3 is that the default file association for .py files got messed up (either overwritten or not set correctly by Python 3’s installer). Here’s how to fix it:

• Right-click any .py script file → Select Open with → Choose another app
• Scroll down and click More apps → Find your preferred Python interpreter (either Python 2 or 3) from the list. If it’s not there, click Look for another app on this PC and navigate to the python.exe file in your Python installation folder (e.g., C:\Python27\python.exe or C:\Python39\python.exe)
• Make sure to check the box that says Always use this app to open .py files to lock in the association.

Pro tip: If you installed Python with the "Install launcher for all users" option (recommended!), you can use the py command to switch versions on the fly without changing associations. Just add #! python2 or #! python3 at the very top of your script, and double-clicking will run it with the specified version.

If your Python 3 path isn’t taking effect, chances are you either added the wrong paths or the order in your PATH is causing conflicts. Here’s the correct way to set it up:

• Open your system environment variables (search "Edit the system environment variables" in Windows search → Click Environment Variables)
• Under System variables, find the Path variable and click Edit
• Add two entries for Python 3:
  • The main installation folder (e.g., C:\Python39)
  • The Scripts folder (e.g., C:\Python39\Scripts—this is where pip3 lives)
• Important: If you want Python 3 to be the default when you type python in the command line, move these Python 3 entries above any Python 2 entries in the Path list. If you want Python 2 as default, keep Python 2’s paths higher up.
• To avoid confusion, you can even rename the executables:
  • Go to your Python 2 folder, rename python.exe to python2.exe
  • Go to your Python 3 folder, rename python.exe to python3.exe
    Now you can type python2 or python3 in the command line to explicitly run the version you want—no more guessing!

If you don’t want to change the default association but need to run a script with a specific Python version, just use the command line:

• For Python 2: python2 your_script.py (or py -2 your_script.py if you have the launcher)
• For Python 3: python3 your_script.py (or py -3 your_script.py)

This is especially useful if you have some scripts that only work with Python 2 and others that need Python 3.

Just remember: Always install Python 2 and 3 in separate folders (never overwrite one with the other) and double-check that both versions’ paths are in your PATH variable. That should eliminate most coexistence headaches!

内容的提问来源于stack exchange，提问作者Tarang Somani