Python script: problems with shebang line (unix)

Question

I am trying to get a feel for the Flask microframework by launching a test application to local server. When trying to run my code, app.py, I keep getting the error message:

-bash: ./app.py: /flask/bin/python: bad interpreter: No such file or directory

Here is the basic code (taken from here) for app.py, which lives in my todo-api directory:

#!/flask/bin/python
from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return "Hello, World!"

if __name__ == '__main__':
    app.run(debug=True)

I've checked the file path to the python interpreter, and it should exist:

:bin $ pwd python

Users/me/Documents/Python/todo-api/flask/bin

I have followed the tutorial to the T; I've tried changing the shebang line to:

#!/flask/bin/python2.x
#!flask/bin/python
#!/flask/bin/env python

But to no avail. I am not that knowledgeable about bash, and have tried looking up what is going on, but the solutions to folks with similar problems have not worked for me; is there something going on behind the scenes that I am not understanding?

Answer 1

Bash shebangs expect an absolute path to the interpreter. So in your case you need to specify the full path to your Python interpreter i.e.:

#!/Users/me/Documents/Python/todo-api/flask/bin

You might want to investigate the use of /usr/bin/env python to be able to use the interpreter that is available in your user's $PATH environment variable. See https://unix.stackexchange.com/questions/12736/how-does-usr-bin-env-know-which-program-to-use/12751#12751

Answer 2

pwd tells you the current directory. It doesn't tell you where a command is located. The output from that command is a red herring.

You may be looking for which python. Put that path into your shebang line. Note that this will give you the Python interpreter from your $PATH, which may or may not be the right one.

The standard shebang line for Python scripts is

#!/usr/bin/env python

or

#!/usr/bin/python

Answer 3

I was having a similar issue with trying to setup a python script as an executable for testing some things and realized that bash was getting in the way more than it was helping. I ended up setting up pyinstaller (which is incredibly easy) and then making my script a stand alone executable without bash being in the mix.

Here's what I did (only takes a couple of minutes and no config): First; pyinstaller needs: build-essential & python-dev

apt-get install build-essential python-dev
(or yum, etc... depending on your OS)

Then use the built in python package manager to setup pyinstaller: pip install pyinstaller

That's it. Run: pyinstaller --onefile myapp.py (or pyinstaller.exe if your OS needs exe)

If it's successful (and it usually is), your new executable will be in a folder "Dist" in the same area you ran pysinstaller.