Difference between revisions of "Short Notes on Python"

Revision as of 13:01, 15 September 2016

Timing, and memory, on Linux

Timing

On Linux, it's safer to use time.time()

import time
t = time.time()
# do some stuff
print "stuff took %1.3f", time.time() - t, "seconds"

On Windows, AFAIK, it's safer to use time.clock()

Memory

For me, the following does a good job getting memory usage (in kB) on Linux:

import resource
print resource.getrusage(resource.RUSAGE_SELF).ru_maxrss

Since resource is standard package, it should work on Windows too, but I don't know if it does, or what units are used if it works.

Importing Files

If you need to import a file '../mylib/commons.py', you can use the following snippet:

import sys, os
fld = os.path.realpath(os.path.abspath(os.path.join('..', 'mylib')))
if fld not in sys.path:
    sys.path.insert(0, fld)
import commons

# use your commons.py module now...
commons.super_function()

uWSGI, nginx, Flask

• install uwsgi (incl. uwsgi python plugin), python flask, and nginx,

Setting Up uWSGI

• create main.py file that will hold the server logic, for instance:

from flask import Flask

app = Flask(__name__)


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

• create uwsgi config file, wsgi.ini (minimal version here; read uwsgi docs for head-spinning array of configurables):

[uwsgi]
module          = main:app
master          = true
processes       = 5
socket          = 127.0.0.1:8000
protocol        = http
plugin          = python

• run uwsgi

uwsgi --ini wsgi.ini

• check that all works on http://localhost:8000/

Adding nginx Layer

• remove the "protocol" directive from wsgi.ini, and add "die-on-term":

[uwsgi]
module          = wsgi:app
master          = true
processes       = 5
socket          = 127.0.0.1:8000
plugin          = python
die-on-term     = true

• add a new vhost to nginx - /etc/nginx/sites-available/app.nginx:

server {
    listen 80;
    server_name my.awesome.domain;
    location / {
        include uwsgi_params;
        uwsgi_pass 127.0.0.1:8000;
    }
}

• • communication through socket is also possible (see socket, chmod-socket, vacuum and other directives for uWSGI)
  • of course, create link in /etc/nginx/sites-enabled/, and restart nginx,

Run uWSGI daemon on boot

• create systemd file for uWSGI, /etc/systemd/system/uwsgi-app.service:

[Unit]
Description=Job that runs the uWSGI app

[Service]
Type=simple
WorkingDirectory=/home/project/flask-test/
ExecStart=/usr/bin/uwsgi --ini wsgi.ini

[Install]
WantedBy=multi-user.target

Then you can start and stop the uwsgi service using:

# systemctl start uwsgi-app.service
# systemctl stop uwsgi-app.service

Once you're happy with the settings, enable the daemon to be run on boot:

# systemctl enable uwsgi-app.service