windows环境用python修改环境变量的注意点（含代码）

1、部分环境变量字段需要保留原来的值，只是做添加，不可以替换

2、Path和PATH对于python来说是一样的，也就是说存在名为Path的环境变量时，添加PATH的环境变量，会覆盖原有的Path环境变量，需要做判断

3、java_home之类的home路径，若原先已存在路径，哪怕已添加路径，系统也只会从第一个路径查找，而不是新添加的路径查找

4、java安装后配置环境变量时，要注意环境变量是配置在哪个用户下面，所有用户公用的是SYSTEM用户的环境变量

5、设定安装路径时，使用C:\而不是C:\\，否则安装后由于tomcat或java的path为C:\\java之类的，导致系统报错

The JAVA_HOME environment variable is not defined correctly
This environment variable is needed to run this program
NB: JAVA_HOME should point to a JDK not a JRE
这个报错也可能是windows的本地环境与远程执行环境不同导致的，为了方便，全部用python调用底层api去运行程序或进程或服务，在运行的bat开头set环境变量，然后解决了

代码如下：

# coding=utf8
import os
import sys
from subprocess import check_call

if sys.hexversion > 0x03000000:
    import winreg
else:
    import _winreg as winreg
import subprocess

def run_cmd(cmd, cwd=None, runas=None):
    u"""
    运行cmd命令。
    """
    if not sys.platform.startswith('win') and runas and runas != 'root':
        cmd = 'su - {} -c "{}"'.format(runas, cmd)
    # logger.info(cmd)
    proc = subprocess.Popen(cmd,
                            stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT,
                            shell=True,
                            cwd=cwd)
    return proc

def get_output(cmd, cwd=None, wait=True, runas=None):
    u"""
    获得命令执行后的标准输出或错误输出。
    """
    proc = run_cmd(cmd, cwd=cwd, runas=runas)
    lines = []
    if wait:
        while proc.poll() is None:
            if proc.stdout:
                lines.extend(proc.stdout.readlines())
    lines.extend(proc.stdout.readlines())
    return lines

class Win32Environment:
    """Utility class to get/set windows environment variable"""

    def __init__(self, scope):
        # assert scope in ('user', 'system')
        self.scope = scope
        if scope == 'user':
            self.root = winreg.HKEY_CURRENT_USER
            self.subkey = 'Environment'
        else:
            self.root = winreg.HKEY_LOCAL_MACHINE
            self.subkey = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'

    def search(self, name):
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_READ)
        key_value = ''
        try:
            i = 0
            while i >= 0:
                key_value, path, value = winreg.EnumValue(key, i)
                i += 1
                if key_value == name:
                    break
        except:
            key_value = ''
        return key_value

    def getenv(self, name):
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_READ)
        try:
            value, _ = winreg.QueryValueEx(key, name)
        except:
            value = ''
        return value

    def setenv(self, name, value):
        # Note: for 'system' scope, you must run this as Administrator
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_ALL_ACCESS)
        winreg.SetValueEx(key, name, 0, winreg.REG_EXPAND_SZ, value)
        winreg.CloseKey(key)
        # For some strange reason, calling SendMessage from the current process
        # doesn't propagate environment changes at all.
        # TODO: handle CalledProcessError (for assert)
        check_call(
            '''\"%s" -c "import win32api, win32con;assert win32api.SendMessage(win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE,0, 'Environment')"''' % sys.executable)

    def get_userenv(self, name):
        # Note: for 'system' scope, you must run this as Administrator
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_ALL_ACCESS)
        value, _ = winreg.QueryValueEx(key, name)
        return value

def set_env_path(env_obj, env_name, env_path,refresh=False):
    need_add = False
    path_values = None
    exist_path = None
    if env_obj.search(env_name):
        exist_path = env_obj.get_userenv(env_name)
    if not exist_path and env_obj.search(env_name.upper()):
        exist_path = env_obj.get_userenv(env_name.upper())

    if refresh:
        exist_path=None
    if exist_path:
        path_values = [i for i in exist_path.split(';')]
        for i in env_path.split(';'):
            if i not in path_values:
                path_values.append(i)
                need_add = True
    if not need_add and path_values:
        return '已添加环境变量{}:{}'.format(env_name, exist_path)

    if path_values:
        env_path = ';'.join(path_values)

    env_obj.setenv(env_name, os.path.expanduser(env_path))
    path_value = env_obj.get_userenv(env_name)
    return '已添加环境变量{}:{}'.format(env_name, path_value)

if __name__ == '__main__':
    env_obj = Win32Environment(scope="SYSTEM")
    print set_env_path(env_obj, 'JAVA_HOME', java_home,refresh=True)

    print set_env_path(env_obj, 'Path', '%JAVA_HOME%\\bin;%JAVA_HOME%\\jre\\bin')

    print set_env_path(env_obj, 'CLASSPATH',
                       '.;%JAVA_HOME%\\lib\\dt.jar;%JAVA_HOME%\\lib\\tools.jar')