我正努力地摆脱这个问题，因为它在上周之前是可以工作的，但不知何故现在无法正常运行。
当我为Google App Engine应用程序设置虚拟环境并使用dev_appserver.py启动应用程序时，我出现了导入标准库时的错误（例如“ImportError: No module named base64”）。
以下是我的操作：
（使用系统Python）
virtualenv --python=python2.5 --no-site-packages ~/.virtualenv/foobar
然后，我将一个gae.pth文件添加到~/.virtualenv/foobar/lib/python2.5/site-packages/中，该文件包含Google App Engine库的信息：
/usr/local/google_appengine
/usr/local/google_appengine/lib/antlr3
/usr/local/google_appengine/lib/cacerts
/usr/local/google_appengine/lib/django
/usr/local/google_appengine/lib/fancy_urllib
/usr/local/google_appengine/lib/ipaddr
/usr/local/google_appengine/lib/webob_1_1_1
/usr/local/google_appengine/lib/yaml/lib
这是基于这个答案的。
然后我激活了我的 "foobar" 虚拟环境，并尝试使用 dev_appserver.py 启动应用程序。
服务器启动了，但第一次请求出现了前面提到的 "ImportError: No module named base64" 错误。如果我访问管理控制台，则会得到 "ImportError: No module named cgi"。
如果我启动 Python，我可以加载这些模块。
>>> import base64
>>> base64.__file__
'/System/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/base64.py'
似乎SDK的沙箱机制阻止了这些库的加载。但就像我之前所说的，直到上周我都可以使用这个功能...不知道发生了什么变化或者我不小心破坏了虚拟环境，我无法弄清楚我最初是如何使其工作的。
软件版本:
Google App Engine SDK 1.3.7
Mac OS X Snow Leopard 10.6.4
virtualenv 1.5.1
更新: 回答Alan Franzoni的问题：
我正在使用Mac OS X自带的系统Python。 我通过easy_install安装了virtualenv。 今天我升级到了virtualenv 1.5.1以尝试修复这个问题。
如果我使用虚拟环境python运行python /usr/local/bin/dev_appserver.py，问题仍然存在。 如果我取消激活虚拟环境并使用系统python2.5运行该命令，则可以正常工作。 （此外，我也可以使用GoogleAppEngineLauncher启动我的应用程序。）
这是完整的堆栈跟踪（此示例使用Kay框架，但使用webapp时问题相同）：
Traceback (most recent call last):
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 3206, in _HandleRequest
self._Dispatch(dispatcher, self.rfile, outfile, env_dict)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 3149, in _Dispatch
base_env_dict=env_dict)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 525, in Dispatch
base_env_dict=base_env_dict)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2402, in Dispatch
self._module_dict)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2312, in ExecuteCGI
reset_modules = exec_script(handler_path, cgi_path, hook)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2208, in ExecuteOrImportScript
exec module_code in script_module.__dict__
File "/Users/look/myapp/kay/main.py", line 17, in <module>
kay.setup()
File "/Users/look/myapp/kay/__init__.py", line 122, in setup
from google.appengine.ext import db
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1287, in Decorate
return func(self, *args, **kwargs)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1937, in load_module
return self.FindAndLoadModule(submodule, fullname, search_path)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1287, in Decorate
return func(self, *args, **kwargs)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1839, in FindAndLoadModule
description)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1287, in Decorate
return func(self, *args, **kwargs)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 1790, in LoadModuleRestricted
description)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", line 81, in <module>
import base64
ImportError: No module named base64