如何用Python脚本检查Python是否已安装？Windows PyInstaller部署场景

需求与现有代码 #

需要编写可通过PyInstaller转为Windows可执行文件的脚本，核心功能为：检查系统是否已安装Python，未安装则自动下载对应架构的Python安装包并执行安装。现有代码已实现下载与安装逻辑，但缺少Python存在性检查部分：

import subprocess, requests, platform

architecture = platform.uname()[4]

if architecture == 'AMD64':
    executable_file = "https://www.python.org/ftp/python/3.11.1/python-3.11.1-amd64.exe"
elif architecture == 'ARM64':
    executable_file = "https://www.python.org/ftp/python/3.11.1/python-3.11.1-arm64.exe"
r = requests.get(executable_file)
with open("python-3.11.1-amd64.exe",'wb') as f:
    f.write(r.content)


cmd = "python-3.11.1-amd64.exe"

returned_value = subprocess.call(cmd, shell=True)
if returned_value == 1602:
    print("Installation Cancelled. Exitting.")
    quit()
print('returned value:', returned_value)

检查Python是否已安装的实现思路 #

方法1：尝试调用Python命令 #

Windows下可通过python或py（Python官方启动器）命令检测：

• 使用subprocess.run调用python --version或py --version，设置check=True捕获异常，若抛出CalledProcessError或FileNotFoundError，则判定Python未安装。

方法2：读取Windows注册表 #

Python安装时会将路径信息写入注册表，可通过winreg模块读取以下路径验证：

• 系统级安装：HKEY_LOCAL_MACHINE\SOFTWARE\Python\PythonCore\<版本号>\InstallPath
• 用户级安装：HKEY_CURRENT_USER\SOFTWARE\Python\PythonCore\<版本号>\InstallPath
  若能读取到有效路径，则说明对应版本Python已安装。

方法3：检查常见安装路径 #

遍历Windows下Python的常规安装目录，判断是否存在python.exe：

• 系统默认路径：C:\Python311（对应3.11版本）
• 用户自定义路径：C:\Users\<用户名>\AppData\Local\Programs\Python\Python311

整合检查逻辑后的完整代码 #

以下是整合了**方法1（命令检测）**的完整脚本，同时修复了原代码中文件名与架构不匹配的问题：

import subprocess
import requests
import platform
import sys

def is_python_installed():
    # 尝试调用python命令
    try:
        subprocess.run(["python", "--version"], check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        return True
    except (subprocess.CalledProcessError, FileNotFoundError):
        # 尝试调用py启动器命令
        try:
            subprocess.run(["py", "--version"], check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            return True
        except (subprocess.CalledProcessError, FileNotFoundError):
            return False

if __name__ == "__main__":
    if is_python_installed():
        print("Python已安装，无需执行安装流程。")
        sys.exit(0)
    
    # 下载对应架构的Python安装包
    architecture = platform.uname()[4]
    if architecture == 'AMD64':
        exe_name = "python-3.11.1-amd64.exe"
        executable_file = f"https://www.python.org/ftp/python/3.11.1/{exe_name}"
    elif architecture == 'ARM64':
        exe_name = "python-3.11.1-arm64.exe"
        executable_file = f"https://www.python.org/ftp/python/3.11.1/{exe_name}"
    else:
        print(f"不支持的系统架构：{architecture}")
        sys.exit(1)
    
    print(f"开始下载Python安装包：{executable_file}")
    r = requests.get(executable_file)
    with open(exe_name, 'wb') as f:
        f.write(r.content)
    
    # 执行安装
    print("开始执行Python安装...")
    returned_value = subprocess.call(exe_name, shell=True)
    if returned_value == 1602:
        print("安装已取消，退出程序。")
        sys.exit(1)
    elif returned_value == 0:
        print("Python安装成功！")
    else:
        print(f"安装过程返回异常值：{returned_value}")

内容的提问来源于stack exchange，提问作者Ruler