IndentationError: unindent does not match any outer indentation level（关键词：Web开发/bug）

简短报错信息：

File "/home/henry/dev/flask_henry/app/auth/views.py", line 18
    flash('Invalid username or password.')
                                         ^
IndentationError: unindent does not match any outer indentation level

完整报错信息：

(venv_flask_henry) henry@henry-virtual-machine:~/dev/flask_henry$ python manage.py 
/home/henry/dev/flask_henry/venv_flask_henry/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py:794: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
  'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
Traceback (most recent call last):
  File "manage.py", line 8, in 
    app = create_app(os.getenv('FLASK_CONFIG') or 'default')
  File "/home/henry/dev/flask_henry/app/__init__.py", line 32, in create_app
    from .auth import auth as auth_blueprint
  File "/home/henry/dev/flask_henry/app/auth/__init__.py", line 5, in 
    from . import views
  File "/home/henry/dev/flask_henry/app/auth/views.py", line 18
    flash('Invalid username or password.')
                                         ^
IndentationError: unindent does not match any outer indentation level

Google Assistant搜索到的错误原因：

IndentationError: unindent does not match any outer indentation level错误表明，你使用的缩进方式不一致，有的是 tab 键缩进，有的是空格缩进，改为一致即可。

参考文献：
1.http://webcache.googleusercontent.com/search?q=cache:o_9wvRMKGoYJ:9425473.blog.51cto.com/9415473/d-3/p-6+&cd=2&hl=zh-CN&ct=clnk&gl=tw&client=aff-cs-360se