Возможности интерпретатора Python в NX-OS

Возможности интерпретатора Python в NX-OS

Anton Tugai

Customer Support Engineer, Cisco TAC

October, 2014

2 © 2013-2014 Cisco and/or its affiliates. All rights reserved.

Cisco Support Community – Expert Series Webcast

Сегодня на семинаре Эксперт Cisco TAC Антон Тугай расскажет о тенденциях в области Cisco SDN и

существующих решениях на данный момент.

Антон Тугай

Инженер центра

технической поддержки

Cisco TAC в Брюсселе


Технические Эксперты

Тема: Возможности интерпретатора Python в NX-OS

Дата проведения вебинара: 21 октября 2014 года

Борис Берлог




Александр Нестеров





Спасибо, что посетили наш вебинар сегодня Сегодняшняя презентация включает опросы аудитории

Пожалуйста, участвуйте!


Спасибо, что присоединились к нам сегодня Скачать презентацию Вы можете по ссылке: https://supportforums.cisco.com/ru/document/12173321

Присылайте Ваши вопросы!

Используйте панель Q&A, чтобы задать вопрос. Наши эксперты ответят на них.


Вопрос №1

Сталкивались ли вы уже с Openflow / SDN / onePK

a) Нет, не слышал ничего

b) Слышал о существовании но не вникал о чем это

c) Слышал, интересовался, имею представление

d) Уже использовал или ближайшее время планируется запуск, внедрение

e) Куда я попал?


Cisco Support Community – Expert Series Webcast

Антон Тугай

Инженер центра технической поддержки Cisco TAC в Брюсселе

Октябрь, 2014

Возможности интерпретатора Python в NX-OS


Несколько слов о Python

Интеграция Python в NX-OS

Примеры и демонстрация

Содержание


Несколько слов о Python


Where does the name python come from ?

Trivia!


Python is an interpreted programming (scripting) language

Available for Linux, Windows, Mac

Two common versions: 2.7(x) and 3.3(x)

2.7 more widely used than 3.3 at the time of writing

Python code is not compiled into standalone binary

It’s either interpreted (interactive shell) or translated into byte code and executed by Python VM

Code can be packaged as a “frozen binary” and executed on systems that don’t have Python installed

the Python VM is packaged within the frozen binary (using py2exe, pyinstaller or freeze)

Basics


Python home page http://www.python.org/

Major Releases Python 3.2.2 September 4, 2011

Python 3.1.4 June 11, 2011

Python 3.0.1 February 13, 2009

Python 2.7.2 June 11, 2011

Python 2.6.7 June 3, 2011

Python 2.5.4 December 23, 2008

Python 2.4.6 December 19, 2008

Python 2.3.7 March 11, 2008

Python 2.2.3 May 30, 2003

Python 2.1.3 April 8, 2002

Python 2.0.1 June 2001

Python 1.6.1 September 2000

Python Distributions

2.7.x is probably the

version most frequently

used today; this slide

deck focuses primarily on

2.7

http://www.python.org/


Python is an interpreted language

no pre-compile step as in Java and C++

each time Python code is run it is interpreted afresh

code changes can be very quickly made and tested

code can also be entered interactively

can dynamically construct Python code

For example in the form of a string and execute it directly

What about performance?

(much) slower than compiled C/C++ .. but also much more flexible

Good enough for most cases

Very large projects such as Openstack are implemented in Python

Modules to measure (profile) performance exist

Python is interpreted


When executing Python instructions, Python internally compiles the source into a format called byte code

This is meant to speed up execution

This process is hidden from the programmer

You will now and then notice .pyc files automatically created in your folders (depending if Python has write access)

Next time you run your code, assuming it hasn’t been modified, Python skips the compilation step and directly runs the byte code inside the Python VM

The Python VM is Python’s runtime engine. It always comes with any installation of Python

Note: VM does not mean a VMware VM here!

Byte code compilation


If you are used to other programming languages that are compiled, you should know there is a significant difference in terms of error checking with interpreted languages

Python checks errors at runtime

This means your code can contain errors such as

if name == ‘Foobar':

print repeeeet(name)

else:

print repeat(name)

as long as name is not Foobar the error won’t get caught!

Keep that in mind, you will get caught!

Interpreted code: error checking


Be aware that Python is case sensitive

A and a are different variables

We’re going to explore variables in a bit

Python programs typically have the .py extension

Run using python <code.py> or python –i <code.py>

In Linux, you can set the execute bit and the proper shebang

typically, let the shell figure out which Python to use with this shebang: #!/usr/bin/env python

Python is case-sensitive


You MUST indent code blocks in Python

Keep this rule in mind, it will catch you almost inevitably if you are already used to other programming languages

There are no curly braces to delimitate code blocks

Code blocks are identified with a colon and indentation

Prefer white spaces to tabs for indentation

Four white spaces is the preferred de-facto standard

http://legacy.python.org/dev/peps/pep-0008/#indentation

Indentation is mandatory


The hash # sign indicates comments follow

Usually ok for short comments

Can start a new line or be used at the end of a line

Comments included at the beginning of your code appear when invoking help(yourscript):

Comments


Your code should contain comments

They should be relatively short and to the point

Comments should say why you are doing what you are doing

The code already says how; why you did things in a certain way is more important

Too many comments hurt readability though and require maintenance – find the right balance

Sidenote: should you write comments?


Why Python?

• CLI has no language structures (loops, conditions), Python provides that.

• Established, Modern and Powerful, Clean, lots of libraries.

TCL: less well-known, archaic, not cool.

Perl: well-known, but hacky, not object-oriented.

• Applications

Embedded Event Manager (EEM)

Power-On Auto-Provisioning (POAP)

Create “Super Commands”

Quick, Interactive, Automation.


Python Integration Overview

• Python Version 2.7.2 Interactive Mode Non-interactive Mode (run scripts)

• Enhanced python: new function: cli(“cli-command”)

For show commands, 3 formats: o Return classical cli output (raw string)

o Return a python dictionary (associative array)

o Direct print to stdout (practical when “playing” interactively)

• Python Exception Handling Syntax Errors Backend Errors

• Sandbox (no linux shell access, except allowed cases)


Интеграция Python в NX-OS


Native python interpreter on nexus

Ability to run python scripts on the nexus switch.

Provides ability to execute CLI commands from your python script.

Python scripts can parse CLI outputs and perform conditional actions

(e.g syslog, shut/no shut, logging etc.)

Integration with EEM.

Call a different python script from a script

Lots of python modules available to import in your code.

No license needed!

No

license

needed

Native Python Available from:

Nexus 5000 – 5.2(1)N1(1)

Nexus 6000 – day 1

Nexus 7000 – 6.1(2)

Nexus 9000 – day 1

Python version :

Nexus 5000 – 2.7.2

Nexus 6000 – 2.7.2

Nexus 7000 – 2.7.2

Nexus 9000 – 2.7.5


Invoking Python on Nexus 7K-5K

Nexus supports Python v2.7.2 version in 2 modes

o interactive mode

o non interactive (script) mode

Interactive Mode

switch# python

Copyright (c) 2001-2012

Python Software

Foundation; All Rights

Reserved

switch# >>> print "hello

world“

hello world

switch# >>> exit()

Non Interactive (script) Mode

Switch # source crc.py

-----------------------------------------

-------

Started running CRC checker

script

finished running CRC checker

script

-----------------------------------------

--------

Switch # dir bootflash:scripts

946 Oct 30 14:50:36 2013

crc.py

7009 Sep 19 10:38:39 2013

myScript.py

22760 Oct 31 02:51:41 2012

poap.py

Type python to

enter

interactive

python

interpreter

How to call a

python script

on nexus 7000.

crc.py script

will be covered

later in the

slides

bootflash:scri

pts directory is

the default

script directory.


Available on N3K, N5K, N6K, N7K in “recent” releases

Available on N9K “standalone” at FCS

Just type “python” at the prompt

Then import cisco and import cli (N9K)

Python interpreter on NxOS


Unfortunately at the time of writing, Python on NXOS isn’t exactly similar across all Nexus platforms

The N9K is leading the effort – modules were simplified and cleaned up, XML output is being flattened for several commands

A significant difference between the N9K and the other platforms is how you invoke CLI commands. On the N9K you import cli and you get three functions: cli, clid and clip

cli.cli returns a string

cli.clid returns a JSON string

cli.clip returns print-friendly CLI output

Not platform independent


How is Python integrated? (1/2)

CLI Interpreter

Python Interpreter

Operator

Console/telnet/ssh

Other nxos component

(bgp, osfp, …)

MTS

VSH

Switch from CLI to Python Interpreter

o Interactive: python / exit

o Non-interactive: source <file>

However, In Python Interpreter,

? and <tab> (online help)

operate on CLI parse-tree py exit Cli()


How is Python integrated? (2/2)

CLI Interpreter

Python Interpreter

Operator

Console/telnet/ssh

Other nxos component

(bgp, osfp, …)

MTS

VSH

• All regular python commands

o May be crippled by sandbox

o to block potentially malicious calls

• New python command “cli()”

o Run cli commands in python

• e.g, cli("show version")

o Takes cli command arg as a string

o Executes the cli command through

• cli interpreter

o Returns results as a string or

• dictionnary

o

Filtered by

sandbox

Results as

a string

CLI commands

as a string

Execution


switch# show clock 23:54:55.872 UTC Wed May 16 2012

switch# python -- enter python interpreter (adding >>> or ... to prompt)

switch# >>> cli(“conf term ; interface loopback 1”)

switch(config-if)# >>> cli(“ip address 1.1.1.1/24”)

switch(config-if)# >>> cli(“exit”) -- exit the cli interface mode

switch(config)# >>> cli(“exit”) -- still in python interp mode

switch# >>> i=0

switch# >>> while i<8: -- composite command -> ‘more input’ prompt (...)

switch# ... i=i+1

switch# ... cmd = "show module %i" % i

switch# ... r=clid(cmd)

switch# ... if "TABLE_modinfo/model" in r.keys():

switch# ... if r["TABLE_modinfo/model"] == "Nurburgring":

switch# ... print "got a racer in slot %d" % i

switch# ... – empty input to indicate end of loop got a racer in slot 3

switch# >>> exit -- return to cli interpreter

switch#


switch# python -- create python interpreter switch# >>> i = 2

switch# >>> print “var i = %d” % i

var i = 2

switch# >>> cli(“configure terminal”)

switch(config)# >>> blabla

switch(config)# >>> exit -- destroy python interpreter switch# - cli interp still at exec mode (“conf t” is lost) switch# python -- new python interp switch# >>> print “var i = %d” % i -- previous python cli mode and vars gone Error: variable ‘i’ undefined.

switch# >>> exit

switch# conf t ; inter lo 1

switch(config-if)# python -- new python interp

switch(config-if)# >>> -- inherits the cli mode (forked from cli).

Python is forked from vsh ->

• No state is preserved between two python invocations

• CLI mode is lost permanently when exiting python


CLI Formats (1/2)

string = cli (“cli-command”) -- returns cli output as a string dictionary = clid (“cli-command”) -- returns a dictionary (if xml output) clip (“cli-command”) -- returns void, prints to stdout

Three formats:

switch# >>> cli("conf ; interface loopback 1")

Enter configuration commands, one per line. End with CNTL/Z.

switch(config-if)# >>> clip('where detail‘)

mode: conf

interface loopback1

username: root

vdc: switch

routing-context vrf: default

switch(config-if)# >>> cli('where detail')

'\x1b[00m mode: conf\n interface loopback1\n username:

root\n vdc: switch\n routing-context vrf: default\n'

switch(config-if)# >>> r = cli('where detail') ; print r

(same output as clip() above!)


switch(config-if)# >>> i=0 switch(config-if)# >>> while i<3: switch(config-if)# ... i=i+1 switch(config-if)# ... cli('ip addr 1.1.1.1/24') switch(config-if)# ... switch(config-if)# >>> cli('end') switch# >>> r = clid('show version') switch# >>> for k in r.keys(): switch# ... print "%30s" % k, " = %s" % r[k] switch# ... cpu_name = Intel(R) Xeon(R) CPU rr_sys_ver = 6.2(0.110) manufacturer = Cisco Systems, Inc. isan_file_name = bootflash:///full rr_ctime = Wed May 16 02:40:57 2012 proc_board_id = JAF1417AGCB bios_cmpl_time = 02/20/10 kickstart_ver_str = 6.1(1) [build 6.1(0.292)] [gdb] isan_tmstmp = 05/16/2012 02:26:02 switch# >>> exit


switch# show file bootflash:scripts/test1.py #!/bin/env python i=0 while i<3: r=clip('show version') uptime_name='/@/show/version/__readonly__/kern_uptm_secs' print uptime_name, r[uptime_name] clid('sleep 1') i=i+1 switch# source test1.py -- default directory is /bootflash/scripts /@/show/version/__readonly__/kern_uptm_secs 36 /@/show/version/__readonly__/kern_uptm_secs 38 /@/show/version/__readonly__/kern_uptm_secs 40 switch#

Default directory of scripts Invoke python


switch(config)# >>> cli("interface loop 1")

switch(config-if)# >>> cli("ip address 1234.1.1.1/24")

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

cisco.cli_syntax_error: % Invalid ip address at '===>' marker:

% ip address 123===>4.1.1.1/24 switch(config-if)# >>> try: cli("ip address 1234.1.1.1/24")

switch(config-if)# ... except: print sys.exc_type, sys.exc_value

switch(config-if)# ... <class 'cisco.cli_syntax_error'> % Invalid ip address at '===>' marker:

% ip address 123===>4.1.1.1/24

switch(config-if)# >>> try: cli("ip address 1.1.1.1/24")


switch(config-if)# ... switch(config-if)# >>> cli("interface loopback 2")

switch(config-if)# >>> try: cli("ip address 1.1.1.1/24")


switch(config-if)# ... <class 'cisco.cli_execution_error'>

% 1.1.1.1/24 overlaps with address configured on loopback1

switch(config-if)# >>>


switch# python Copyright (c) 2001-2012 Python Software Foundation; All Rights Reserved

switch# >>> import os switch# >>> os.getcwd() '/bootflash' switch# >>> os.chdir("/isan/bin") Permission denied. Traceback (most recent call last): File "<stdin>", line 1, in <module> OSError: [Errno 13] Permission denied: '/isan/bin' switch# >>> os.system("cd /isan/bin") system(cd /isan/bin): rejected! -1 switch# >>> f=open("/isan/bin/vsh", "r") Permission denied. Traceback (most recent call last): File "<stdin>", line 1, in <module> IOError: [Errno 13] Permission denied: '/isan/bin/vsh' switch# >>> f=open("/bootflash/alias", "r") switch# >>>

• Block potentially harmful function calls


An “online help protocol” allows script to provide online help, man-page and context sensitive variants

switch# source ? abc No help script is not supporting the online help protocol cgrep 'context grep': shows matching line plus the context lines (to be used behind a pipe, for show-run type of output) Example of context for 'ip address 1.1.1.1/24': ‘eth 2/1’ find-if Find interfaces that match selected attribute values (from 'show intf br') ntimes Runs specified command specified numbers of times redo-history This is run a list of commands from the history again show-if Show selected interface attributes show-version A better 'show version' sys/ Directory here you find example scripts, packaged in image switch# source ntimes ? filename can be abbridged if unique (or tabbed) arg1: the command, in quotes arg2: number of times to run the commands <CR> > Redirect it to a file >> Redirect it to a file in append mode | Pipe command output to filter


The script is called with the following argument: __cli_script.*help __cli_script_help : request to return a one line description of the script’s purpose

__cli_script_args_help : request to return help for arguments, filename is passed as first argument, as well as any arguments entered so far

__cli_script_args_help_partial: the last argument is ‘partial’. E.g. “token?” instead of “token ?”. Argument help return formats: classical (“type|description” left|right side”):

print "ftp|Use ftp for file transfer protocol" print "scp|Use scp for file transfer protocol" exit(0)

Man Page style (simpler to implement, but no tabbing).

print "__man_page" print " whatever…“


Python Introspection on Cisco Extension

>>> import cisco >>> cisco.__doc__ 'contains commands that integrate with Cisco CLI' >>> dir(cisco) ['__doc__', '__name__', '__package__', 'cli', 'clid', 'clip'] >>> cisco.cli.__doc__ 'execute a cli command, return the lines of output as char*' >>> cisco.clid.__doc__ 'execute a cli command, return name/value pairs (d: dictionary)' >>> cisco.clip.__doc__ 'execute a cli command, just dump to stdout, return void to python (p: print)' >>>

>>> [(a,type(cisco.__getattribute__(a))) for a in dir(cisco)] [('__doc__', <type 'str'>), ('__name__', <type 'str'>), ('__package__', <type 'NoneType'>), ('cli', <type 'builtin_function_or_method'>), ('clid', <type 'builtin_function_or_method'>), ('clip', <type 'builtin_function_or_method'>)] >>>


Backgrounding a script

switch# source background sleep 100 switch# source background sleep 50 switch# show background username . terminal pid start time script args ... root . . pts/0 7687 03:31 00:00:00 sleep.py 90 . root . . pts/0 7696 03:31 00:00:00 sleep.py 50 . switch# kill background ? WORD Background script to terminate, by process-id or just a regex matching any line from 'show background' output switch# kill background 7687 switch# show background username . terminal pid start time script args ... root . . pts/0 7696 03:31 00:00:00 sleep.py 50 . switch# switch# exit Linux(debug)# su john switch# kill background 7696 bash: line 1: kill: (7696) - Operation not permitted switch#


Expect

switch# python Copyright (c) 2001-2012 Python Software Foundation; All Rights Reserved switch# >>> import pexpect switch# >>> child=pexpect.spawn("vsh") -- only vsh allowed

switch# >>> child.sendline("show clock") 11 switch# >>> child.expect(".*2012") 0 switch# >>> print child.after show clock switch# show clock 03:44:12.620 UTC Wed Sep 26 2012 switch# >>>


Importing Python Libraries Containing cli()

You need to import the ‘cisco’ module

(done automatically by ‘python’ or ‘source’ command, but not by

‘import’ command).

File time.py:

from cisco import cli def show_clock: cli(“show clock”)

File stuff.py:

import time time.show_clock()


Вопрос №2

После полученной информации ваш интерес к SDN

a) У меня и так все работает, не хочу усложнять и строить космический корабль

b) Интересно, возможно протестирую в свободное время

c) Заинтересован, займусь изучением вопроса и попробую запустить

d) У нас уже используется либо проводятся тесты

e) До сих пор не понимаю о чем идет речь


Вопрос №3

О чем было бы интересно узнать на следующем вебинаре о SDN

a) Контроллерные решения на основе Cisco XNC

b) Cisco и OpenStack совместные решения

c) APIC / ACI / Insieme / Nexus 9000

d) VxLAN

Отправьте свой вопрос сейчас!

Используйте панель Q&A, чтобы задать вопрос. Эксперты ответят на Ваши вопросы.

Получить дополнительную информацию, а также задать вопросы эксперту в рамках данной темы Вы можете на странице, доступной по ссылке:

https://supportforums.cisco.com/community/russian/expert-corner

Вы можете получить видеозапись данного семинара и текст сессии Q&A в течении ближайших 5 дней по следующей ссылке

https://supportforums.cisco.com/community/russian/expert-corner/webcast




https://supportforums.cisco.com/community/netpro/ask-the-expert/webcasts





Вебинар на русском языке

Тема: Базовая настройка Device Provisioning и отладка основных проблем при использовании Cisco TMS Provisioning Extension

во вторник, 25 ноября, в 12.00 мск Присоединяйтесь к эксперту Cisco

Михаилу Щекотилову

В рамках сессии будет проведена демонстрация базовой

настройки Device Provisioning на Cisco VCS и TMS, а также

разобраны основные ошибки, которые при этом

встречаются, и показаны методы и инструменты для их

отладки.


https://supportforms.cisco.com/community/russian

http://www.facebook.com/CiscoSupportCommunity

http://twitter.com/#!/cisco_support

http://www.youtube.com/user/ciscosupportchannel

https://plus.google.com/110418616513822966153?prsrc=3#110418616513822966

153/posts

http://itunes.apple.com/us/app/cisco-technical-support/id398104252?mt=8

https://play.google.com/store/apps/details?id=com.cisco.swtg_android

http://www.linkedin.com/groups/CSC-Cisco-Support-Community-3210019

Newsletter Subscription: https://tools.cisco.com/gdrp/coiga/showsurvey.do?surveyCode=589&keyCode=146298_2&PH

YSICAL%20FULFILLMENT%20Y/N=NO&SUBSCRIPTION%20CENTER=YES



http://twitter.com/#!/cisco_support














https://tools.cisco.com/gdrp/coiga/showsurvey.do?surveyCode=589&keyCode=146298_2&PHYSICAL FULFILLMENT Y/N=NO&SUBSCRIPTION CENTER=YES

https://tools.cisco.com/gdrp/coiga/showsurvey.do?surveyCode=589&keyCode=146298_2&PHYSICAL FULFILLMENT Y/N=NO&SUBSCRIPTION CENTER=YES


• Русском https://supportforums.cisco.com/community/russian

• Испанском https://supportforums.cisco.com/community/5591/comunidad-de-

soporte-de-cisco-en-espanol

• Португальском

https://supportforums.cisco.com/community/5141/comunidade-de-suporte-

cisco-em-portugues

• Японском http://www.csc-china.com.cn/

https://supportforums.cisco.com/community/russian

https://supportforums.cisco.com/community/russian

https://supportforums.cisco.com/community/5591/comunidad-de-soporte-de-cisco-en-espanol














https://supportforums.cisco.com/community/5141/comunidade-de-suporte-cisco-em-portugues












http://www.csc-china.com.cn/




Спасибо за Ваше время

Пожалуйста, участвуйте в опросе

Date post:	15-Jun-2015
Category:	Technology
Upload:	cisco-russia
View:	371 times
Download:	2 times

Возможности интерпретатора Python в NX-OS

Technology