Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I'm following the Flask tutorial here:

http://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world

I get to the point where I try ./run.py and I get:

Traceback (most recent call last):
  File "./run.py", line 3, in <module>
    from app import app
  File "/Users/benjaminclayman/Desktop/microblog/app/__init__.py", line 1, in <module>
    from flask import Flask
ImportError: No module named flask
This looks similar to:
ImportError: No module named flask
But their solutions aren't helpful.  For reference, I do have a folder named flask which one user mentioned may cause issues.
                @MalikBrahimi When I run Python and then import flask and check what version I have installed, it gives back "0.10.1".  So it looks like I have it installed...
– anon_swe
                Jul 6, 2015 at 18:16
                You're saying if you run python and then do import flask you have no errors? Is it possible you have to versions of python on your computer?
– ari
                Jul 6, 2015 at 18:21
                Can you insert import sys; print sys.path in that file (before the line where the error happens) and also run that in the interactive prompt?
– ari
                Jul 6, 2015 at 18:25
                @ari I tried to do the virtual environment thing but may have messed it up somehow?  and yes, I'm using Python 3.3 but think I have 2.7 floating around
– anon_swe
                Jul 6, 2015 at 18:50
                You aren't using version 3, you are using version 2, and you have two copies of Python version 2 on your mac, one that came with OSX, and the other that you installed. So, all in all - it looks like you have three versions of Python; Python3, Python2 (you installed), Python2 (came with the system). Sounds like you aren't using the correct environment here; where you have installed Flask is not the system default, and this is likely the cause of your headache.
– Burhan Khalid
                Jul 6, 2015 at 19:27
Try deleting the virtualenv you created.  Then create a new virtualenv with:
virtualenv flask
Then:
cd flask
Now let's activate the virtualenv
source bin/activate
Now you should see (flask) on the left of the command line.
Edit: In windows there is no "source" that's a linux thing, instead execute the activate.bat file, here I do it using Powershell: PS C:\DEV\aProject> & .\Flask\Scripts\activate)
Let's install flask:
pip install flask
Then create a file named hello.py (NOTE: see UPDATE Flask 1.0.2 below):
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
    return "Hello World!"
if __name__ == "__main__":
    app.run()
and run it with:
python hello.py
UPDATE Flask 1.0.2
With the new flask release there is no need to run the app from your script.  hello.py should look like this now:
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
    return "Hello World!"
and run it with:
FLASK_APP=hello.py flask run
Make sure to be inside the folder where hello.py is when running the latest command.
All the steps before the creation of the hello.py apply for this case as well
                Hi, I'm very new for python.  Everything just works fine with virtualenv in terminal. But, my problem is I'm using IDE Atom... can atom run the code at the same virtualenv environment?
– boog
                Feb 13, 2019 at 7:56
                Yes this works! Instead of doing pip install flask (which is for python 2), if you are using python3, you need to use pip3 install flask or other extensions of flask. To change your python version, you can use alias python="python3".
– Agent 0
                May 6, 2019 at 2:52
The only way I could solve was by adding my users python dir to myapp.wsgi file. As an example:
sys.path.append('/home/deployer/anaconda3/lib/python3.5/site-packages')
I guess that if you install the packages in the global enviroment, you should have no problem, but I had my python packages installed as user.
                or by doing this export PYTHONPATH=/root/environments/my_env/lib/python3.6/site-packages/
– Carlos Oliveira
                Dec 16, 2019 at 0:25
                Not sure why this is working, probably something to do with the path.  Any insight on this?
– nscalf
                Mar 22, 2019 at 1:15
pip install flask
Another gotcha is that sometimes people type pip install Flask with the cap F
Posting this here in case somebody gets stuck.
Let me know if it helped.
Useful Link:
What is the difference between pip install and sudo pip install?
If you're using virtualenv it's a good idea to 
pip freeze >> requirements.txt 
to allow for the installed packages to be listed in one place.
The sudo command and -H flag. For more on sudo's -H flag, look at Paul's answer.
Hope this helps you.
                Ah its the simple things. I had the wrong libapache mod wsgi in my dockerfile after upgrading to python 3... have a +1
– Craicerjack
                Sep 21, 2017 at 15:16
/etc/apache2/sites-available/FlaskApp.conf
Add the following two lines before the "WSGIScriptAlias" line:
WSGIDaemonProcess FlaskApp python-home=/var/www/FlaskApp/FlaskApp/venv/FlaskApp
WSGIProcessGroup FlaskApp
Restart Apache:service apache2 restart
I'm following the Flask tutorial too.And I met the same problem.I found this way to fix it.
http://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world
In my case the solution was as simple as starting up my virtual environment like so:
$ venv/scripts/activate
It turns out I am still fresh to Python :)
Go to the flask file in microblog, then activate the virtual environment with source bin/activate, then go to flask/bin and install flask, and the rest of the packages, pip install flask. You will see flask listed inside bin directory. Try to run ./run.py again from microblog (or from wherever you have the file).
If you are using Pycharm then this is the virtual environment issue.
So, at the time of creating your Python project you will have to select "Existing interpreter" option -> click "system Interpreter" -> select the correct option for example "*\AppData\Local\Programs\Python\Python3.6\python.exe".
You can use 'New Virtual Env' as well, but I have just given the quick fix that should work for Pycharm users.
it will print your path. Check wether flask is installed in the sys.path.
For MacOS, python path is under 
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
But pip'll install python package by default under
/Library/Python/2.7/site-packages
That's why it doesn't work for MacOS.
The flask script is nice to start a local development server, but you would have to
restart it manually after each change to your code. That is not very nice and Flask can
do better. If you enable debug support the server will reload itself on code changes,
and it will also provide you with a helpful debugger if things go wrong.
To enable debug mode you can export the FLASK_DEBUG environment variable before
running the server:
forexample your file is hello.py
$ export FLASK_APP=hello.py
$ export FLASK_DEBUG=1
$ flask run
in my case using Docker, my .env file was not copied, so the following env vars were not set: 
.env.local:
FLASK_APP=src/app.py
so in my Dockerfile i had to include:
FROM deploy as dev
COPY env ./env
which was referenced in docker-compose.yml 
env_file: ./env/.env.local
another thing i had to pay attention to is the path variable to ensure my environment is used
ENV PATH $CONDA_DIR/envs/:my_environment_name_from_yml_file:/bin:$CONDA_DIR/bin:$PATH```
I had a similar problem using WSL and PyCharm / VSCode, the problem only occurred in the development environment and not in production. I realized that IDE's with WSL can have problems when exporting PYTHONPATH from their work directory and I started to do it manually.
Before running your program and inside a VENV, try running the following command:
export PYTHONPATH="path/my_user/code"
                Hi... I am facing the same error. I have tried everything answered above, still getting same error. Could you please tell me how to do it manually. I am using VS Code. Python 3.9.5, flask 2.0.1
– sandeep
                Jul 27, 2021 at 15:39
                Hey bro! Try using the command in the edited comment, and tell me about success or failed
– Enderson Menezes
                Jul 28, 2021 at 19:33
In your case , the solution is  :
First:
Open the  terminal and navigate to the directory/folder where that python file is located ( in ur case the python file you created is run.py) and make sure you have installed flask in that same directory/folder.
Second :
Now , type the following command :
$python3   "pythonfilename" (in ur case, its $python3  "run.py")
I had the same error where it said flask module not found. this is what I did:
used venv to create a virtual environment $ python3.6 -m venv --without-pip virtual
activated the virtual environment using source virtual/bin/activate
downloaded pip into the virtual environment curl https://bootstrap.pypa.io/get-pip.py | python
installed flask using pip install flask
after running my application, all was good.
                As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
– Community
                Jun 10, 2022 at 15:51
Found that answer here: https://stackoverflow.com/a/49748494/3197202
Then I could just install flask:
pip install flask