已通过pip安装的模块在Python3可用，Python2不可用，如何解决？

I’ve run into this exact Python package isolation issue before, so let me walk you through what’s going on and how to fix it:

The Problem Scenario #

• You successfully installed the apted module (version 1.0.3) using:

  pip install apted
  

• Testing with Python 2.7 threw an error:

  python -m apted -t {a{b}{c}} {a{b{d}}} -mv
  # Output: No module named apted
  

• But the same test worked flawlessly with Python 3:

  python3 -m apted -t {a{b}{c}} {a{b{d}}} -mv
  # Outputs distance, runtime, and tree transformation results as expected
  

Why This Happens #

In environments with both Python 2.7 and Python 3 installed, the pip command usually defaults to linking with your system’s Python 3 installation. That means when you run pip install apted, the module gets placed in Python 3’s site-packages directory—completely unreachable for Python 2.7, even though the module claims compatibility with 2.7.

The Fix #

The solution is simple: explicitly use Python 2.7’s dedicated pip executable to install the module. Run this command:

pip2 install apted

This ensures apted is installed directly into Python 2.7’s package directory, making it accessible whenever you use the python (Python 2.7) interpreter.

内容的提问来源于stack exchange，提问作者sten