Flask Hello World error

Question

I installed Python, Flask following these articles in CentOS 6.6

https://github.com/h2oai/h2o/wiki/Installing-python-2.7-on-centos-6.3.-Follow-this-sequence-exactly-for-centos-machine-only

http://flask.pocoo.org/docs/0.10/installation/

http://flask.pocoo.org/

Now When I am running hello.py ie

    from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == "__main__":
    app.run()

I got this error

Traceback (most recent call last):
  File "hello.py", line 1, in <module>
    from flask import Flask
ImportError: No module named 'flask'

Is there anything that needs to be done to run Flask beside that is provided in those documentation?

Thanks

Answer 1

The code is correct, so probably you haven't installed Flask globally.

Have you installed through sudo apt-get install python-virtualenv or through easy_install ?

Answer 2

I had my hello.py in /opt/myproject/flask/hello.py I had my venv in /opt/myproject/flask/venv

In /opt/myproject/flask I was doing . venv/bin/activate . venv/bin/activate and running the python hello.py .

But once I went to /opt/myproject/flask/venv and did . bin/activate . bin/activate and came back to /opt/myproject/flask and ran python hello.py everything came out fine.

Answer 3

Obviously as mentioned above you haven't installed flask yet.

Essentially if you create too many projects, then use virtualenvwrapper where you can list your environments by executing the command:

workon

Access your env like this:

workon myenv

Think of any project to be encapsulated from other project by wrapping all the packages inside a virtual environment and this env needs to be activated before running the project. Any module/package you import in your project should be preinstalled inside your environment by using this example below:

pip install Flask
pip install SQLAlchemy

And you can list your packages inside your environment by executing this command:

pip list

Usually you should have all the packages added to your requirements.txt to keep track on things and make it easy to install from scratch by executing this command:

pip install -r requirements.txt

Follow these simple steps and you'll be on the safe side always!

Happy coding, J.