如何限制requirements.txt仅在Python3环境执行，Python2执行时报错？

Great question! Here are a few reliable ways to make sure your dependency installation only works in Python 3, with clear error prompts for Python 2 users:

1. Add Python version constraints directly in requirements.txt #

The simplest approach is to include a version check at the top of your requirements.txt file. This leverages pip's built-in support for environment markers (available in pip ≥9.0.0):

# requirements.txt
python_version >= "3.0"

# Your actual dependencies below
requests>=2.25.1
numpy>=1.21.0
pandas>=1.3.0

When someone runs pip install -r requirements.txt in Python 2, pip will throw an error like:

ERROR: Could not find a version that satisfies the requirement python_version>=3.0 (from versions: none)
ERROR: No matching distribution found for python_version>=3.0

Pros: No extra scripts needed, works cross-platform.
Cons: Requires pip 9.0.0 or newer (most modern environments have this, but older setups might not).

2. Use a wrapper Python script for installation #

For more control over the error message and compatibility with older pip versions, create a small Python wrapper script (e.g., install.py):

#!/usr/bin/env python3
import sys
import subprocess

def main():
    # Check if running Python 3
    if sys.version_info < (3, 0):
        print("❌ Error: This installation requires Python 3.x. You're using Python {}.{}.".format(sys.version_info[0], sys.version_info[1]))
        sys.exit(1)
    
    # Execute the pip install command using the current Python interpreter
    try:
        subprocess.check_call([sys.executable, "-m", "pip", "install", "-r", "requirements.txt"])
        print("✅ Dependencies installed successfully!")
    except subprocess.CalledProcessError:
        print("❌ Failed to install dependencies.")
        sys.exit(1)

if __name__ == "__main__":
    main()

Tell users to run this script instead of directly using pip:

python install.py

Pros: Custom, user-friendly error messages; ensures you're using the same Python interpreter for both the check and installation; works everywhere Python runs.
Cons: Adds an extra file to your project.

3. Use platform-specific shell scripts #

If your users are mostly on Linux/macOS or Windows, you can write shell scripts to handle the version check:

For Linux/macOS (install.sh) #

#!/bin/bash
# Get the major Python version
PY_MAJOR=$(python -c "import sys; print(sys.version_info[0])")

if [ "$PY_MAJOR" -ne 3 ]; then
    echo "❌ Error: This installation requires Python 3. You're using Python $PY_MAJOR."
    exit 1
fi

pip install -r requirements.txt

Make it executable and run:

chmod +x install.sh
./install.sh

For Windows (install.bat) #

@echo off
python -c "import sys; exit(0 if sys.version_info[0]==3 else 1)"
if errorlevel 1 (
    echo ❌ Error: This installation requires Python 3.
    exit /b 1
)

pip install -r requirements.txt

Run it with:

install.bat

Pros: Familiar for users comfortable with shell/batch scripts; no Python wrapper needed.
Cons: Platform-specific (you'll need both scripts if supporting multiple OSes).

内容的提问来源于stack exchange，提问作者Vishal