WFE603Programming in Python

Rob FaludiCollaborative Strategy Leader

Session Overview

• Problem Statement• Python Programming Language (v. 2.4)• Python on Digi devices• Digi ESP

The Problem

• Putting application intelligence in the right places

• Writing simply• Writing experimentally• Writing powerfully

Where’s Your Application?

• Open-source, flexible language that puts decision-making smarts on a gateway

• Very simply to write basic code• Easy to experiment interactively• Powerful extensions• Broad support

• High-level• Readable• Dynamically typed• Automatic memory management• Scripting, OOP, functions• Extensible• Powerful• Portable• Free

Zen of Python• Beautiful is better than ugly.• Explicit is better than implicit.• Simple is better than complex.• Complex is better than complicated.• Flat is better than nested.• Sparse is better than dense.• Readability counts.• Special cases aren't special enough

to break the rules.• Although practicality beats purity.• Errors should never pass silently.• Unless explicitly silenced.

• In the face of ambiguity, refuse the temptation to guess.

• There should be one-- and preferably only one --obvious way to do it.

• Although that way may not be obvious at first unless you're Dutch.

• Now is better than never.• Although never is often better than

*right* now.• If the implementation is hard to explain,

it's a bad idea.• If the implementation is easy to explain,

it may be a good idea.• Namespaces are one honking great idea

-- let's do more of those!

• Less is more– Less to type– Less to debug– Less to maintain

• Productivity

Lots of Resources

• Online– Python.org (http://docs.python.org)– Dive Into Python (http://diveintopython.org)– Python Challenge (http://www.pythonchallenge.com)

• Books– Learning Python by Mark Lutz– Programming Python by Mark Lutz– Python Cookbook by Alex Martelli, Anna Martelli

Ravenscroft, David Ascher

A basic program

def hello(): """Prints a salutation to the user""" # Say hello print "Hello World!"

if __name__ == "__main__": hello()

Note that indentation dictates structure, not keywords or special tokens.

Really basic

print "Hello World!"

Python is about getting work done

print "Hello World!"

print 2+2

foo="bar"

print foo

Indentation Matters

if 1+1==2: print "answer correct!" print "you did math!"

if 1+1==3: print "answer correct"

print "you did math!"

Core Data Types

• Numbers• Strings• Lists• Dictionaries• Tuples• Files

Data types – Scalars

• Numbers– Three types (int, float and long)– Varying representations (10, 0xa, 012)– Don't worry too much about type (except division)– 5 /2 = 2– 5.0 / 2 = 2.5– from __future__ import division

• bool– Values ( True and False )

• None

Container Objects

• Sequences– Strings: mystring ="abcdefg"– Lists: foo=[1, 'a', None]– Tuples: bar=(1, 'a', None) (immutable)

• Mapping– Dictionaries: moof={"a": True, 42: 7}

Strings

• Normal – "Hello\nThere" (allows escapes)• Triple-quoted (preserves entered text)"""HelloThere"""• Raw – r"Hello\nThere" (escapes ignored)• Unicode – u"\u0496"(inserts Җ)

– Allows unicode escapes, creates unicode strings, a different type

• Many native operations plus normal immutable sequence operations

dir shows available attributes>>> f= 37.1>>> g="hello"

>>> dir(f)['__abs__', '__add__', '__class__', '__coerce__', '__delattr__', '__div__', '__divmod__', '__doc__', '__eq__', '__float__', '__floordiv__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__int__', '__le__', '__long__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__nonzero__', '__pos__', '__pow__', '__radd__', '__rdiv__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rmod__', '__rmul__', '__rpow__', '__rsub__', '__rtruediv__', '__setattr__', '__str__', '__sub__', '__truediv__']

>>> dir(g)['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__str__', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'replace', 'rfind', 'rindex', 'rjust', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill’]

Conditional Execution

if <expr>: <…>elif <expr>: <…>else <expr>: <…>

There is no goto or case statement in Python

Loops

for <var> in <sequence>: <…>

while <expr>: <…>

Variations:• break and continue affect looping• pass can act as a placeholder• (x)range(i[, j[, k]]) is extremely useful for for statements

Functionsdef arg_info(arg=42, *pos_args, **kw_args): """Doc-string""" if (arg == 42): print "arg has default value"

# Print positional arguments for i in len(pos_args): # Use string formatting operator print "Positional argument %d is %v" % (i, pos_args[i])

print "Keyword arguments" for key in kw_args.keys(): print "\t", key, ": ", kw_args[key]

return len(pos_args) + len(kw_args)

Modules

• We already have seen one# hello.pydef hello(): """Prints a salutation to the user""" # Say hello print "Hello World!"

if __name__ == "__main__": hello()

import hellohello.hello()

Importing

• Styles– from <module> import <name>– import <module> as <alias>

• Uses sys.path to find

Exceptions and Error Handling

class ItCantWork(Exception): pass

def no_work(): raise ValueError

try: no_work()except ValueError, e: # handle exception does_work()else: raise ItCantWork

Homework

• Classes• Generators• Iterators• List comprehensions• The standard library• Lots of other useful things…

• Where do I configure Python on the Digi device?– Applications -> Python in the WebUI– Manage scripts and module files on the device– Configure Python scripts to run automatically on boot

– Python in iDigi Manager Pro– Manage scripts and module files on the device– Configure Python scripts to run automatically on boot

– Python command line tools– set python – Configure automatic start with added options– python – Run scripts manually, or enter an interactive session

Using Digi Python

• Plain Text Files• use .py extension• upload files

• iDigi• web UI• command line interface

Putting Files on the Device

• Check the Box• iDigi• web UI• command line interface

• Command Line Launch• from CLI: set python• or from within Python: import <filename>

Launching a Program

Purpose: Configures Python programs to execute on device boot.

Syntax: set python [range=1-4] [state={on|off}] [command=filename,args]

Options: range=1-4 Range specifies the index or indices to view or modify with the command. state={on|off}When the state is set to on, the specified command is run when the device boots. command=filename,argsThe program filename to execute and any arguments to pass with the program, similar to the arguments for the python command. The command option allows for programs to be run from a TFTP server; however, this usage is not recommended. If there are spaces to provide arguments, make sure to wrap the entire command in quotation marks.

set python

• terminal% telnet 192.168.1.200• Trying 192.168.1.200...• Connected to 192.168.1.200• Escape character is '^]'.

• #> python

• >>>

Running Interpreter

Monitoring the System

Management -> Connections

• For monitoring only, can't disconnect Python activity• Equivalent functionality in the CLI is the who command

Checking Resources (Memory)

• The memory of the system is all the memory there is (no virtual memory), use it wisely.

• The rest of the system uses memory as well, leave some for it (~400-500k at least)

Checking Resources (Sockets)

128 max in the entire system

Garbage Collection

• Simplest:– Run gc.collect() as often as "you find necessary".

• Tune thresholds (gc.set_threshold)– "correct" values vary widely per application

• Don't use __del__ methods• If you must, break cycles manually by

examining gc.garbage periodically and using your object knowledge to resolve the cycle

Viewing Debug Output

#> set trace state=on mask=printf:*

All sys.stdout and sys.stderr output from your script will beredirected to the console that ran trace.

Digi Python

XBee® SocketsCreation:from socket import *s = socket(AF_XBEE, SOCK_DGRAM, XBS_PROT_TRANSPORT)

• XBee sockets are datagram sockets like UDP• Maximum packet length depends on radio technology and configuration

Address format:

(address_string, endpoint, profile_id, cluster_id)

zigbee/zb_ex1_hello.py, zb_ex2_rw.py

XBee Moduleddo_command(addr_extended, id[, param, timeout,

order=False, apply=True)ddo_set_param(…)ddo_get_param(…) – No param argument

Get/set DDO parameters on XBee modules– addr_extended – Address of node to configure– id – Two letter string identifying parameter– param – New value to set for ddo_command or ddo_set_param– timeout – Max time to wait for response– order – Force this request not to run concurrently– apply – Make changes active (Same as "AC" id)

Returns: ddo_command and ddo_get_param return binary string configuration value. ddo_set_param returns boolean success. All versions throw an exception if they cannot reach the radio.

XBee (cont…)get_node_list(<refresh>) -> list of node objects

• Performs device discovery– refresh

• False: returns the gateways cache of nodes.• True: Blocks to perform fresh discovery

• Node object attributes– type: One of coordinator, router or end– addr_extended, addr_short: Address representations– addr_parent: Parent's short address– profile_id, manufacturer_id: Identifying characteristics– label: Nodes 'NI' parameter– device_type: Nodes 'DD' parameter

zigbee/zb_ex4_disc.py

File system

• Path structure is <VOLUME>/<path>• System volume is WEB• Python modules go in WEB/python• Directory listing/traversal may be limited– listdir, mkdir will be available in FW version

2.9

• USB volumes progress A, B, ...– Not guaranteed to enumerate the same each boot

• Python file objects work completely.

Digicli Module

import digiclidigicli.digicli(<cmd>) -> (status, output)Run a CLI command

– cmd – Command to run

Returns– status – False if command failed– output – list of output lines from execution

Perform a Network Node Discovery # Perform a node discovery and print out# the list of discovered nodes to stdio.

# import the zigbee module into its own namespaceimport zigbee

# Perform a node discovery:node_list = zigbee.getnodelist() # Print the table: print "%12s %12s %8s %24s" % \

("Label", "Type", "Short", "Extended")print "%12s %12s %8s %24s" % \

("-" * 12, "-" * 12, "-" * 8, "-" * 24) for node in node_list:

print "%12s %12s %8s %12s" % \(node.label, node.type, node.addr_short, node.addr_extended)

Use DDO to Read Temperature from XBee Sensor

# Collect a sample from a known XBee Sensor adapter# and parse it into a temperature.

# import zigbee and xbee_sensor modules:import zigbeeimport xbee_sensor

# configure known destination:DESTINATION="[00:13:a2:00:40:0a:07:8d]!"# ensure sensor is powered from adapter:zigbee.ddo_set_param(DESTINATION, 'D2', 5)zigbee.ddo_set_param(DESTINATION, 'AC', '')

# get and parse sample:sample = zigbee.ddo_get_param(DESTINATION, '1S')xbee_temp = xbee_sensor.XBeeWatchportT()xbee_temp.parse_sample(sample)print "Temperature is: %f degrees Celsius" % (xbee_temp.temperature)

Digicli Example

import digicli status, output = digicli.digicli('show net') if status: for line in output: if line.find('MAC Address') >= 0: l = line.split(':') print "".join(l[1:]).strip()import

digiclidigicli.digicli(<cmd>) -> (status, output)

The Digi ESP

The Digi ESP• An IDE used across several product lines, built on top of Eclipse• Facilitates development with Digi products• Distributed as a built-in product (not as plug-ins)• Powerful editing capabilities (syntax highlight, auto completion, syntax

verification, …); Code builders and checkers; Integrated symbolic debugger• Example/Project wizards• Configuration tools• Extended through custom plug-ins to provide a better integration with our

products• Bundled with other components needed like JVM, Python interpreters, etc• Multiplatform (runs on MS Windows, Linux and Mac)

The Digi ESP

ESP flavors

Digi ESP for Python

Digi ESP for NET+OS

Digi ESP for Embedded Linux

Digi ESP for Python• Complete and simplified development process:

– Easy-to-use project wizards– Python source code and Smart iDigi Dia Editor– Build management– Remote launch/debug– Application deployment

• Built-in iDigi support • Full integrated help with interactive tutorials• Additional tools:

– Device discovery (USB, LAN and iDigi)– Remote file explorer– Channel explorer– Terminal consoles– Package manager

Package Manager Server

Digi

InternetDigi ESP for Embedded

Linux

Digi ESP for NET+OS

Digi ESP for

Python

Package Manager

• Digi ESP software distribution/upgrade plug-in• Allows the access to the different software packages available on the PkM

server, available for that specific ESP flavor, accordingly to the privileges provided by the installed PkM license(s)

• Packages are created by Digi engineers which are later posted to the Package Manager server, making them available to all Digi ESP users

• Package Types:– New features– Fixes– Documentation– Updates– Other

Getting ESP

• www.digi.com/esp

Using ESP

• connecting devices• Hello World• SMTP• HTTP• Dia Example

Digi Python Samples

Connect a Device

Hello World"""\ Hello World! demo for Digi devices This example prints out a "Hello World!" message to stdout. """

import sys, os

print "Hello World!"

SMTP AlarmSMTP_Server = "email.mydomain.com" #hostname of the SMTP server sender_email = "test@digi.com" #The sender's email addressrecipient_email = "my@email.com" #The destination email addresssubject = "Value Detect test" #Subject of the emailmsg_format = 'The value is now: %s' #The body of the email, the sample will #replace the %s in this message.

print "Creating alarm"email_alarm = alarm.SMTPAlarm(alarm_function, msg_format, debounce_function, SMTP_Server, sender_email, recipient_email, subject)

Fetch Web Page"def main(): # Open the web page. fhandler = urllib.urlopen(WEB_PAGE) # Print some details about the page retrieved page_info = fhandler.info() print "Retrieved '%s'\r\n" %fhandler.geturl() for item in page_info.items(): print "%s : %s" %(item[0], item[1]) print "\r\nPage content:" # Start reading and printing the content of the web page. while True: data = fhandler.read(1024) if len(data) == 0: break sys.stdout.write(data)

Dia

Using Digi Python

• Where can I get more information?– Digi developer Wiki (http://www.digi.com/wiki/developer)– "Digi Python Programmer's Guide" in particular– Digi support forum (http://www.digi.com/support/forum)– Drop-In Networking -> Software -> Python

• What version of Python should I use?– Python 2.4 for Digi NDS devices.– Python 2.7 for Digi X2E devices.

THANK YOU!

Rob Faludirob.faludi@digi.com