Python – calling a python function from flask app

I am developing an app that runs (always – it is a controller for a heat pump system) in python and I use flask to provide a user interface to controll the app.

The flask app has different control items, for instance buttons to turn the system on or off.

I am trying to execute a specific function from a python module in response to a "click" on a button (the final goal is to change a value in an mmap resource that will be read in another module to change the state of the system).

In the flask app I have something like:

    @app.route('/cntr_hpauto',methods=['GET','POST'])
    @basic_auth.required
    def cntr_hpauto():
        manage_globals.set_from_web()
        return render_template('control.html',cur_hp_mode="auto")

However, this generates an "internal server error'

The complete flask app is (manage_globals is the *.py file I want to import and that contains the function I want to call):

from flask import Flask, request, render_template
from flask_basicauth import BasicAuth

import sys
import os
import mmap
import manage_globals

app = Flask(__name__)

app.config['BASIC_AUTH_USERNAME'] = '***'
app.config['BASIC_AUTH_PASSWORD'] = '***'

basic_auth = BasicAuth(app)

@app.route('/')

def splash():
        return render_template('splash.html')

@app.route('/dashboard', methods=['GET','POST'])
@basic_auth.required
def dashboard():
        return render_template('dashboard.html')

@app.route('/control',methods=['GET','POST'])
@basic_auth.required
def control():
    return render_template('control.html',cur_hp_mode="none")

@app.route('/cntr_hpauto',methods=['GET','POST'])
@basic_auth.required
def cntr_hpauto():
    manage_globals.set_from_web()
    return render_template('control.html',cur_hp_mode="auto")

@app.route('/cntr_hpon',methods=['GET','POST'])
@basic_auth.required
def cntr_hpon():
    return render_template('control.html',cur_hp_mode="on")

@app.route('/cntr_hpoff',methods=['GET','POST'])
@basic_auth.required
def cntr_hpoff():
    return render_template('control.html',cur_hp_mode="off")

if __name__ == '__main__':
    app.run(ssl_context=('/home/groenhol/certs/groenhol.pem', '/home/groenhol/certs/groenhol.key'))

And the module (example, only writing the map file to a logfile) is:

# 14/08/2017 henk witte / groenholland
# part of geotech project, ann controller dual source heat pump
# this module maintains the global database with mmap

import mmap

""" the mmap file is position dependent!
use readlines and split

    line 1: heatpump auto/on/off
    line 2: userpump off
    line 3: srcselect air
"""
def init_conf_file():
    dummy="a"

def set_from_web():
    with open("geotech.conf", "r+b") as f:
        mm = mmap.mmap(f.fileno(), 0)
        for line in iter(mm.readline, b''):
            with open("globals.log","ab") as f2:
                f2.write(line)
    f2.close()
    mm.close()

if __name__ == '__main__':
    init_conf_file()

The flask app runs fine without the function call, the module I import by itself runs fine as well.

Any help much appreciated!

Henk

As suggested by Kevin Pasquarella I added app.debug = true. However, as the error occurs when apache is loadin the main splash page already (apache server error) this did not help. But I then looked at the apache error log:

[Tue Aug 15 21:33:14.638580 2017] [mpm_event:notice] [pid 959:tid 3067240448] AH00489: Apache/2.4.18 (Ubuntu) OpenSSL/1.0.2g mod_wsgi/4.5.17 Python/3.4 configured -- resuming normal operations
[Tue Aug 15 21:33:14.639152 2017] [core:notice] [pid 959:tid 3067240448] AH00094: Command line: '/usr/sbin/apache2'
[Tue Aug 15 21:33:19.825211 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676] mod_wsgi (pid=2461): Target WSGI script '/home/groenhol/py_control/ui/webapp/main.wsgi' cannot be loaded as Python module.
[Tue Aug 15 21:33:19.826502 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676] mod_wsgi (pid=2461): Exception occurred processing WSGI script '/home/groenhol/py_control/ui/webapp/main.wsgi'.
[Tue Aug 15 21:33:19.967421 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676] Traceback (most recent call last):
[Tue Aug 15 21:33:19.970377 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676]   File "/home/groenhol/py_control/ui/webapp/main.wsgi", line 4, in <module>
[Tue Aug 15 21:33:19.970581 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676]     from main import app as application
[Tue Aug 15 21:33:19.971031 2017] [wsgi:error] [pid 2461:tid 3031819312] [remote 192.168.178.85:9676]   File "/home/groenhol/py_control/ui/webapp/main.py", line 41

I then searched for mod_wsgi cannot be loaded as python module

Answers indicate there is a difference between the python version I am using (3.4) and the wsgi version.

So I checked the wsgi version in /etc/apache2/mods-enabled/mod-wsgi.load:

LoadModule wsgi_module "/home/groenhol/miniconda3/lib/python3.4/site-packages/mod_wsgi/server/mod_wsgi-py34.cpython-34m.so"
WSGIPythonHome "/home/groenhol/miniconda3"

So seems to use python 3.4 version.

To make sure I use ldd as I found during the search:

groenhol@arm:~/mod_wsgi-4.5.15$ ldd LoadModule wsgi_module "/home/groenhol/miniconda3/lib/python3.4/site-packages/mod_wsgi/server/mod_wsgi-py34.cpython-34m.so"
LoadModule:
ldd: ./LoadModule: No such file or directory
wsgi_module:
ldd: ./wsgi_module: No such file or directory
/home/groenhol/miniconda3/lib/python3.4/site-packages/mod_wsgi/server/mod_wsgi-py34.cpython-34m.so:
        linux-vdso.so.1 =>  (0xbee90000)
        libpython3.4m.so.1.0 => /home/groenhol/miniconda3/lib/libpython3.4m.so.1.0 (0xb6d40000)
        libpthread.so.0 => /lib/arm-linux-gnueabihf/libpthread.so.0 (0xb6d0f000)
        libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0xb6c23000)
        /lib/ld-linux-armhf.so.3 (0x7f64d000)
        libdl.so.2 => /lib/arm-linux-gnueabihf/libdl.so.2 (0xb6c10000)
        libutil.so.1 => /lib/arm-linux-gnueabihf/libutil.so.1 (0xb6bfd000)
        libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0xb6b85000)
        libgcc_s.so.1 => /lib/arm-linux-gnueabihf/libgcc_s.so.1 (0xb6b5c000)
groenhol@arm:~/mod_wsgi-4.5.15$ WSGIPythonHome "/home/groenhol/miniconda3"
-bash: WSGIPythonHome: command not found

As far as I can tell (http://modwsgi.readthedocs.io/en/develop/user-guides/checking-your-installation.html#python-shared-library) this seems OK?

Ok, so next step?