python 无法运行烧瓶应用程序

Question

我已经满足flask依赖如下。

indikau@ruhuna ~ $ sudo -H python -m pip install flask
Requirement already satisfied (use --upgrade to upgrade): flask in /usr/local/lib/python2.7/dist-packages
Requirement already satisfied (use --upgrade to upgrade): itsdangerous>=0.21 in /usr/local/lib/python2.7/dist-packages (from flask)
Requirement already satisfied (use --upgrade to upgrade): click>=2.0 in /usr/local/lib/python2.7/dist-packages (from flask)
Requirement already satisfied (use --upgrade to upgrade): Werkzeug>=0.7 in /usr/local/lib/python2.7/dist-packages (from flask)
Requirement already satisfied (use --upgrade to upgrade): Jinja2>=2.4 in /usr/local/lib/python2.7/dist-packages (from flask)
Requirement already satisfied (use --upgrade to upgrade): MarkupSafe>=0.23 in /usr/lib/python2.7/dist-packages (from Jinja2>=2.4->flask)
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.
indikau@ruhuna ~ $ ls

这是我的代码。

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello() -> str:
    return 'Hello Flask!'

app.run()

我能够创建一个新的虚拟环境。

indikau@ruhuna ~/Documents/head_first_python/chapter04 $ virtualenv flask
Using base prefix '/usr'
New python executable in /home/indikau/Documents/head_first_python/chapter04/flask/bin/python3.5
Also creating executable in /home/indikau/Documents/head_first_python/chapter04/flask/bin/python
Installing setuptools, pip, wheel...done.
indikau@ruhuna ~/Documents/head_first_python/chapter04 $ which flask
/usr/local/bin/flask

但我仍然收到以下错误。

indikau@ruhuna ~/Documents/head_first_python/chapter04 $ python hello.py 
Traceback (most recent call last):
  File "hello.py", line 1, in <module>
    from flask import Flask
ImportError: cannot import name 'Flask'

有人可以帮助我吗？ （我在python3.x上）

Answer 1

如果要使用 virtualenv，则必须激活虚拟环境。在virtualenv flask之后执行以下代码：

source /home/indikau/Documents/head_first_python/chapter04/flask/bin/activate

并在虚拟环境flask中重新安装flask。