Python
python
tutorial
2.10.1 Subprograms
One of the most important in mathematics concept is to use functions. Functions in computer languages implement mathematical functions. The executing function produces one or more results, which are dependent by the parameters passed to it.
In general, a function is a structuring element in the programming language which groups a set of statements so they can be called more than once in a program. Programming without functions will need to reuse code by copying it and changing its different context. Using functions enhances the comprehensibility and quality of the program. It also lowers the memory usage, development cost and maintenance of the software.
Different naming is used for Functions in programming languages, e.g. as subroutines, procedures or methods.
Python language defines function by a def statement. The function syntax looks:
def function-name(Parameter list):
statements, i.e. the function body
Function bodie can contain one or more return statement. It can be situated anywhere in the function body. A return statement ends the function execution and returns the result, i.e. to the caller. If the return statement does not contain expression, the value “None” is returned.
Python
def Fahrenheit(T_in_celsius):
""" returns the temperature in degrees Fahrenheit """ return (T_in_celsius * 9 / 5) + 32
for t in (22.6, 25.8, 27.3, 29.8):
print(t, ": ", fahrenheit(t))
Output:
Python
>>> 22.6 : 72.68 25.8 : 78.44 27.3 : 81.14 29.8 : 85.64 >>>
jupyter on python3
is installed in omen www/environments/jup
tim@omen:/d/fs/www/environments$ pyvenv jup tim@omen:/d/fs/www$ cd environments/ tim@omen:/d/fs/www/environments$ . jup/bin/activate (jup) tim@omen:/d/fs/www/environments$ jupyter notebook (jup) tim@omen:/d/fs/www/environments/jup/bin$ deactivate
accessing object properties
status ={}
status['pond'] = {'spot': 'center', 'state': 'off', 'tleft': 0, 'nexton': 9}
status['pond']['tleft']= 16
parsing u'5'
basic tutorial
running app forever - supervisorctl
cascada
- port = 8087
- /home/pi/mypi/cascada/server/cascada.py
cascada2
- port = 8088
- /home/pi/mypi/cascada/server/cascada2.py
<markdown>
sudo`supervisorctl` reads configuration from `/etc/supervisor/conf.d` and runs whatever files if finds there.
a typical `conf` ile looks like:
[program:cascada2] command=/usr/bin/python /home/pi/mypi/cascada/server/cascada2.py directory=/home/pi/mypi/cascada/server autostart=true autorestart=true startretries=3 stderr_logfile=/var/log/cascada/cascada2.err.log stdout_logfile=/var/log/cascada/cascada2.out.log user=root environment=SECRET_PASSPHRASE='this is secret',SECRET_TWO='another secret'
you may have to `>supervisor reload` then `ctrl c` the `sudo supervisorctl` to get a new program running forever
</markdown>
pi@raspberrypi ~ $ sudo supervisorctl cascada RUNNING pid 2273, uptime 7 days, 3:17:36
tail -f /var/log/cascada/cascada.out.log tail -f /var/log/cascada/cascada.err.log
after changing cascada.py
pi@raspberrypi ~ $ sudo supervisorctl cascada RUNNING pid 2273, uptime 7 days, 3:17:36 supervisor> stop cascada
exit w ctrl C
sudo lsof -i :8087 sudo kill -9 21118 (kill whatever port lsof returns)
pi@raspberrypi ~ $ sudo supervisorctl cascada STOPPED Jul 16 04:34 PM supervisor> start cascada cascada: started supervisor>
exit w ctrl C ??
- nohup python app.py &
- use screen
- run supervisord(link) on system startup and control all through it (pythonic way :))
nohup means: do not terminate this process even when the stty is cut off.
& at the end means: run this command as a background task.
SSE - Server Side Events
http://flask.pocoo.org/snippets/116/
https://github.com/stevenewey/ssedemo
for node
https://www.npmjs.com/package/simple-sse (has room,haven't tried)
https://tomkersten.com/articles/server-sent-events-with-node/
http://www.futureinsights.com/home/real-time-the-easy-way-with-eventsource-angularjs-and-nodejs.html
SocketIO
http://stackoverflow.com/questions/17641602/how-to-emit-to-room-in-socket-io
