导入错误：在虚拟环境中找不到flask.ext.sqlalchemy模块

当我试图从flask_sqlalchemy导入SQLAlchemy并运行以下代码时，我遇到了主要错误：

Traceback (most recent call last):
  File "/home/jsnyder10/.local/bin/flask", line 11, in 
sys.exit(main())
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 513, in main
cli.main(args=args, prog_name=name)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 380, in main
return AppGroup.main(self, *args, **kwargs)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/core.py", line 697, in main
rv = self.invoke(ctx)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/core.py", line 1066, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/decorators.py", line 64, in new_func
return ctx.invoke(f, obj, *args[1:], **kwargs)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 423, in run_command
app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 152, in __init__
self._load_unlocked()
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 176, in _load_unlocked
self._app = rv = self.loader()
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 237, in load_app
rv = locate_app(self.app_import_path)
  File "/home/jsnyder10/.local/lib/python3.5/site-packages/flask/cli.py", line 90, in locate_app
__import__(module)
  File "/home/jsnyder10/Documents/CS50/pset7/pset7/finance/application.py", line 2, in 
from flask_sqlalchemy import SQLAlchemy
ImportError: No module named 'flask_sqlalchemy'

我不确定这是否相关，但是当我更新sqlaclhemy时，pip会发出以下警告。我尝试更新pip，但由于某种原因，版本9.0.1显示已升级，但实际上没有更新。

You are using pip version 8.1.1, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

当我运行pip list时，以下是我的输出。您可以看到已安装sqlalchemy和flask-sqlalchemy。

DEPRECATION: The default format will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.
appdirs (1.4.3)
click (6.7)
Flask (0.12.1)
Flask-SQLAlchemy (2.2)
itsdangerous (0.24)
Jinja2 (2.9.6)
MarkupSafe (1.0)
packaging (16.8)
pip (9.0.1)
pyparsing (2.2.0)
setuptools (35.0.2)
six (1.10.0)
SQLAlchemy (1.1.9)
Werkzeug (0.12.1)
wheel (0.29.0)

我猜它是使用了错误的Python版本。我没有找到这个问题的根本原因，但是清除我的虚拟机并创建一个新的解决了它。感谢大家的帮助，但我希望我能够解决它。