Category: python

Python Institute PCEP™ – Certified Entry-Level Python Programmer (Exam PCEP-30-02) – EXAM

PCEP™ – Certified Entry-Level
Python Programmer
(Exam PCEP-30-02) – EXAM
SYLLABUS

Certified Associate in Python Programming

Resource links

  • Syllabus – https://pythoninstitute.org/assets/627e61bc29de3989767095.pdf
  • https://pythoninstitute.org/pcep

Infrastructure as Code

Infrastructure as Code

ToolKit

Example Code

Research

Learning Python

Installing Python and a IDE

  • Download and install  from https://www.python.org/downloads/
  • Add Python path environment variblesl control  sysadm.cpl ; c:\python..
  • install Virtualnv; pip install virtualenv
  • Install Microsoft code and Python extension
  • setx /M path “%path%;C:\ProgramData\Python 3.10”
  • [code]
  • #!/usr/bin/env python3
  • print(“hello world!:0
  • [/code]

Learning Resources

  • Existing Blog http://www.detectx.com.au/learning-python-for-networking/
  • Python Kirk Byers (Outlook / Python)
  • Oriely 
  • Linked
  • Acloud Guru

Python Kirk Byers

The second half of this course includes some important content for improving your Python programming. In particular, Class6 on Functions and Namespaces, Class8 on Modules, and Class9 on Classes and Objects.

In this email of Learning Python we are going to cover the following:

I. Introduction Week6
video http://youtu.be/sjYBE6EWwuc
Length is 3 minutes

II. Functions, Part1
video http://youtu.be/i1MzASLYOZY
Length is 12 minutes

III. Namespaces
video http://youtu.be/r8U3_KkvKtw
Length is 10 minutes

IV. Functions, Part2
video http://youtu.be/pRaVagkh9l8
Length is 12 minutes

Additional content that you may be interested in

There is a good chapter on functions in “Learn Python the Hard Way” (I would stop after you finish, “What You Should See”).
http://learnpythonthehardway.org/book/ex18.html

Darren O’Connor has a blog on “Defined Functions – Python”.
http://mellowd.co.uk/ccie/?p=5118

 

Exercises

Reference code for these exercises is posted on GitHub at:
https://github.com/ktbyers/pynet/tree/master/learnpy_ecourse/class6

1. Create a function that returns the multiplication product of three parameters–x, y, and z. z should have a default value of 1.
a. Call the function with all positional arguments.
b. Call the function with all named arguments.
c. Call the function with a mix of positional and named arguments.
d. Call the function with only two arguments and use the default value for z.
2. Write a function that converts a list to a dictionary where the index of the list is used as the key to the new dictionary (the function should return the new dictionary).

3a.Convert the IP address validation code (Class4, exercise1) into a function, take one variable ‘ip_address’ and return either True or False (depending on whether ‘ip_address’ is a valid IP). Only include IP address checking in the function–no prompting for input, no printing to standard output.

3b. Import this IP address validation function into the Python interpreter shell and test it (use both ‘import x’ and ‘from x import y’).

4. Create a function using your dotted decimal to binary conversion code from Class3, exercise1. In the function–do not prompt for input and do not print to standard output. The function should take one variable ‘ip_address’ and should return the IP address in dotted binary format always padded to eight binary digits (for example 00001010.01011000.00010001.00010111). You might want to create other functions as well (for example, the zero-padding to eight binary digits).

5. Write a program that prompts a user for an IP address, then checks if the IP address is valid, and then converts the IP address to binary (dotted decimal format). Re-use the functions created in exercises 3 and 4 (‘import’ the functions into your new program).

 

Class Outline

I. Introduction
A. Why write functions?

II. Functions Part1
A. Function with no parameters
1. Syntax and structure
2. Calling the function
3. Return value
4. Using the return value
5. Docstrings

B. Function with parameters
1. Syntax
2. Default values

C. Various ways of passing arguments to functions
1. Positional arguments
2. Named arguments
3. Mixing positional and named arguments

III. Python Namespaces
A. Functions create their own namespace
B. Name resolution order

IV. Functions Part2
A. Using lists and dicts as function arguments
B. Importing a function

Learning Python 8 Week course

 

  • Week1 – Why Python, the Python Interpreter Shell, and Strings
  • Week2 – Numbers, Files, Lists, and Linters
  • Week3 – Conditionals and Loops
  • Week4 – Dictionaries, Exceptions, and Regular Expressions
  • Week5 – Functions and the Python Debugger
  • Week6 – Netmiko Basics
  • Week7 – Jinja2 Basics, Introduction to YAML and JSON, Complex Data Structures
  • Week8 – Libraries, Package Installation, and Virtual Environments

Video Archive

Week1
Introduction and Some Questions
What is the Nature of Python
Interpreter Shell, Variables, and Assignment
Strings

Week2
Introduction
Print and raw_input
Numbers
Lists and Tuples
Booleans

Week3
Introduction
If Conditionals
For Loops
Passing Arguments into a Script

Week4
Introduction
While Loops
Dictionaries
Exceptions

Week5
Class Review (weeks 1 – 4)

Week6IntroductionFunctions, Part1NamespacesFunctions, Part2

  • https://www.youtube.com/watch?v=XLKkx_U5rNw&list=PLGvd694GjkI-HOAplS6bEkh-IwhwAXM-e
  • https://pyneng.readthedocs.io/en/latest/contents.html

Learning Python for Networking

Learning Python for Networking

Python the Hardway – https://learnpythonthehardway.org/book/?__s=ng1wguqfgy4mttisodvu

Python2 vs Python3 (relevant differences for beginners):
http://www.cs.carleton.edu/faculty/jgoldfea/cs201/spring11/Python2vs3.pdf

Darren O’Connor has a recent blog post about passing arguments into a Python script (Darren is a dual-CCIE, JNCIE who has some blog posts about Python):
http://mellowd.co.uk/ccie/?p=5126

For more complicated argument parsing check out Argparse (requires Python 2.7) or getopt:
https://docs.python.org/2/howto/argparse.html

Getting Python Installed

You will need a system that has Python2.7 on it.

MacOS X
If you are running a recent version of MacOS X, then you will already have Python 2.7 (launch Terminal and type ‘python’ at the prompt).

Linux
Just type ‘python’ from the shell and verify it has Python2.7.

Windows
If you are running on Windows, then you should be able to download and install it from here:

https://www.python.org/downloads/release/python-2712/

Either the ‘Windows x86-64 MSI Installer’ or the ‘Windows x86 MSI Installer’ is probably the right choice.

You might also want to update your Windows system Path so that your computer knows how to find the Python interpreter.  You should be able to find this process online (for your version of Windows).

Web

You can also use an online Python Interpreter (at least for some of the course). You can find one online at http://repl.it/languages/Python.

IDE

Network Config Templating using Ansible

The general problem is this: you want a systematic way of creating network device configurations based on templates and variables.

As background, Ansible is an open-source automation application that can be used to automate many tasks in your environment (predominantly compute and cloud tasks). Ansible can also generate files based on Jinja2 templates and variables. Jinja2 is a widely-used Python templating system, see http://jinja.pocoo.org/ for more information about Jinja2.
Thus, Ansible has all the components for network configuration templating built into it.  This is a very good initial use case for Ansible for network engineers.

Part1 – https://pynet.twb-tech.com/blog/ansible/ansible-cfg-template.html

Part2 – https://pynet.twb-tech.com/blog/ansible/ansible-cfg-template-p2.html

Part3 – https://pynet.twb-tech.com/blog/ansible/ansible-cfg-template-p3.html

Week 1

  1. Introduction and Some Questions
    video https://vimeo.com/119478712
    Length is 11 minutes
    The ‘Some Questions’ section continues into the first 1:12 of the next video
  2. Characteristics of Python
    video https://vimeo.com/119480935
    Length is 7 minutes
  3. Interpreter Shell, Variables, and Assignment
    video http://youtu.be/6ja4KlejT-g
    Length is 8 minutes
  4. Strings
    video http://youtu.be/ItIE8hItji8
    Length is 19 minutes

Week 2

  1. Introduction (Week2)
    video http://youtu.be/uqGZXPfX00E
    Length is 2 minutes
  2. Print and raw_input
    video http://youtu.be/pEXUxySxygg
    Length is 14 minutes
  3. Numbers
    video http://youtu.be/n5ZO8rRcWbA
    Length is 12 minutes
  4. Lists and Tuples
    video http://youtu.be/nUOMXXhQgZQ
    Length is 14 minutes
  5. Booleans
    video http://youtu.be/gCpRBt7pw-0
    Length is 5 minutes

Week 3

  1. Introduction Week  https://vimeo.com/120754390
  2. If Conditionals  http://youtu.be/5lHWv9hkSn8
  3. For Loops http://youtu.be/VR0ggQuClOM
  4. Passing Arguments into a Script http://youtu.be/mUt0uJmD9y4

Week 4

  1. Introduction Week 4  http://youtu.be/UJmDynoQxps
  2. While Loops http://youtu.be/xnZzrnAQdG
  3. Dictionaries http://youtu.be/iGVJmUXcLtI
  4. Exceptions http://youtu.be/fCkjmtIq7wU

SNMP

In this article, I briefly introduce Python and SNMP using the pysnmp library.

I assume that you already have some knowledge on SNMP including MIBs and OIDs.  If not, you should be able to find this information fairly easily on the Internet.

In order to get started, you need to install the pysnmp library.  For context, I am testing on an AWS AMI server (RedHat based i.e. yum instead of apt).

For installation just use ‘pip’:
# As root or sudo (or in a virtual environment)
$ pip install pysnmp

I also installed net-snmp to simplify testing and to add an easy way to perform an SNMP walk.  The installation method for net-snmp will vary depending on your system.

# As root or sudo
$ yum install net-snmp
$ yum install net-snmp-utils

To keep things simple I am only going to use SNMPv1/2c (i.e. this article does not cover SNMPv3).  This is obviously not secure.

Now that I have the pysnmp library installed, the next step is to verify that I can communicate with my test router using SNMP.  First, let’s test this directly from the Linux command line:

$ snmpget -v 2c -c <COMMUNITY> <IP_ADDR> .1.3.6.1.2.1.1.1.0
SNMPv2-MIB::sysDescr.0 = STRING: Cisco IOS Software, C880 Software (C880DATA-UNIVERSALK9-M), Version 15.0(1)M4, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Fri 29-Oct-10 00:02 by prod_rel_team
The OID .1.3.6.1.2.1.1.1.0 is the MIB-2 sysDecr object.  During testing I had multiple problems getting SNMP to work on the router including that I had Cisco’s Control Plane Policing enabled (ooops) and that I needed to allow access through both an edge ACL and through a separate SNMP ACL.

At this point, I am able to communicate using SNMP from my AWS server to my test router.

Now let’s try the same thing except using the pysnmp library.  In order to simplify this I have created a couple of SNMP helper functions see:

https://github.com/ktbyers/pynet/tree/master/snmp/snmp_helper.py

First we need to do some initialization:

>>> from snmp_helper import snmp_get_oid,snmp_extract
>>>
>>> COMMUNITY_STRING = ‘<COMMUNITY>’
>>> SNMP_PORT = 161
>>> a_device = (‘1.1.1.1’, COMMUNITY_STRING, SNMP_PORT)

This code loads my two functions (snmp_get_oid and snmp_extract); it also creates a tuple named ‘a_device’ consisting of an IP, community string, and port 161.

I then call my snmp_get_oid function using the OID of MIB-2 sysDescr:
>>> snmp_data = snmp_get_oid(a_device, oid=’.1.3.6.1.2.1.1.1.0′, display_errors=True)
>>> snmp_data
[(MibVariable(ObjectName(1.3.6.1.2.1.1.1.0)), DisplayString(hexValue=’436973636f20494f5320536f6674776172652c204338383020536f6674776172652
02843383830444154412d554e4956455253414c4b392d4d292c2056657273696f6e2031352e302831294d
342c2052454c4541534520534f4654574152452028666331290d0a546563686e6963616c20537570706f72
743a20687474703a2f2f7777772e636973636f2e636f6d2f74656368737570706f72740d0a436f7079726967
68742028632920313938362d3230313020627920436973636f2053797374656d732c20496e632e0d0a436
f6d70696c6564204672692032392d4f63742d31302030303a30322062792070726f645f72656c5f74656
16d’))]
I can see that I received SNMP data back albeit in an ugly format.  I can now use the snmp_extract function to display the output in a more friendly way.

>>> output = snmp_extract(snmp_data)
>>> print output
Cisco IOS Software, C880 Software (C880DATA-UNIVERSALK9-M), Version 15.0(1)M4, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Fri 29-Oct-10 00:02 by prod_rel_team

Now, let’s repeat this process but using a different OID.  Using snmpwalk on the ‘interfaces’ MIB and the Cisco SNMP Object Navigator, I was able to determine that the OID = .1.3.6.1.2.1.2.2.1.16.5 corresponded to the output octets on FastEthernet4.

Here I query that OID a couple of times in fairly quick succession (less than a minute between queries):
>>> snmp_data = snmp_get_oid(a_device, oid=’.1.3.6.1.2.1.2.2.1.16.5′, display_errors=True)
>>> output = snmp_extract(snmp_data)
>>> print output
293848947

>>> snmp_data = snmp_get_oid(a_device, oid=’.1.3.6.1.2.1.2.2.1.16.5′, display_errors=True)
>>> output = snmp_extract(snmp_data)
>>> print output
293849796

You can see that the count incremented.

Week 5

Videos

I. Class Review (weeks 1 – 4)
video https://vimeo.com/121951502
Length is 16 minutes

Exercises

In these two exercises, I am going to use the following diagram and CDP data:
Diagram
CDP data

Disclaimer: the CDP data is from a test switch and a test router. I have manually modified this data to be consistent with the above diagram.
Reference code for these exercises is posted at:
https://github.com/ktbyers/pynet/tree/master/learnpy_ecourse/class5

1. Parse the CDP data (see link above) to obtain the following information: hostname, ip, model, vendor, and device_type (device_type will be either ‘router’, ‘switch’, or ‘unknown’).

From this data create a dictionary of all the network devices.

The network_devices dictionary should have the following format:

network_devices = {
‘SW1’: { ‘ip’: ‘10.1.1.22’, ‘model’: ‘WS-C2950-24’, ‘vendor’: ‘cisco’, ‘device_type’: ‘switch’ },
‘R1’: { ‘ip’: ‘10.1.1.1’, ‘model’: ‘881’, ‘vendor’: ‘Cisco’, ‘device_type’: ‘router’ },
…
‘R5’: { ‘ip’: ‘10.1.1.1’, ‘model’: ‘881’, ‘vendor’: ‘Cisco’, ‘device_type’: ‘router’ },
}

Note, this data structure is a dictionary that contains additional dictionaries.  The key to the outer dictionary is a hostname and the data corresponding to this key is another dictionary.  For example, for ‘R1’:

>>> network_devices[‘R1’]
{‘ip’: ‘10.1.1.1’, ‘model’: ‘881’, ‘vendor’: ‘Cisco’, ‘device_type’: ‘router’}

You can access a given attribute in the inner dictionary as follows:
>>> a_dict[‘R1’][‘ip’]
‘10.1.1.1’

If this is confusing, you might want to experiment with it in the Python shell:

##### Python Shell – experimenting with dictionary of dictionaries #####

# Initialize network_devices to be a blank dictionary
>>> network_devices = {}

# Assign the key ‘R1’ to network_devices using a value of a blank dictionary (in other words, I am adding a key:value pair to network_devices where the key is ‘R1’ and the value is {} )
>>> network_devices[‘R1’] = {}

# Look at network_devices at this point
>>> network_devices
{‘R1’: {}}

# Add the ‘ip’ and ‘vendor’ fields to the inner dictionary
>>> network_devices[‘R1’][‘ip’] = ‘10.1.1.1’
>>> network_devices[‘R1’][‘vendor’] = ‘Cisco’
>>> network_devices
{‘R1’: {‘ip’: ‘10.1.1.1’, ‘vendor’: ‘Cisco’}}

##### Python Shell – experimenting end #####

For the output to this exercise, print network_devices to standard output.  Your output should look similar to the following (six network devices with their associated attributes).

{‘R1’: {‘device_type’: ‘Router’,
‘ip’: ‘10.1.1.1’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R2’: {‘device_type’: ‘Router’,
‘ip’: ‘10.1.1.2’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R3’: {‘device_type’: ‘Router’,
‘ip’: ‘10.1.1.3’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R4’: {‘device_type’: ‘Router’,
‘ip’: ‘10.1.1.4’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R5’: {‘device_type’: ‘Router’,
‘ip’: ‘10.1.1.5’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘SW1’: {‘device_type’: ‘Switch’,
‘ip’: ‘10.1.1.22’,
‘model’: ‘WS-C2950-24’,
‘vendor’: ‘cisco’}}

2. Create a second program that expands upon the program from exercise 1.

This program will keep track of which network devices are physically adjacent to each other (physically connected to each other).

You will accomplish this by adding a new field (adjacent_devices) to your network_devices inner dictionary.  adjacent_devices will be a list of hostnames that a given network device is physically connected to.  

For example, the dictionary entries for ‘R1’ and ‘SW1’ should look as follows:

‘R1’: {‘IP’: ‘10.1.1.1’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},

‘SW1’: {‘IP’: ‘10.1.1.22’,
‘adjacent_devices’: [‘R1’, ‘R2’, ‘R3’, ‘R4’, ‘R5’],
‘device_type’: ‘Switch’,
‘model’: ‘WS-C2950-24’,
‘vendor’: ‘cisco’},

For the output to this exercise, print network_devices to standard output.  Your output should look similar to the following (six network devices with their associated attributes including ‘adjacent_devices’).

{‘R1’: {‘IP’: ‘10.1.1.1’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R2’: {‘IP’: ‘10.1.1.2’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R3’: {‘IP’: ‘10.1.1.3’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R4’: {‘IP’: ‘10.1.1.4’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘R5’: {‘IP’: ‘10.1.1.5’,
‘adjacent_devices’: [‘SW1’],
‘device_type’: ‘Router’,
‘model’: ‘881’,
‘vendor’: ‘Cisco’},
‘SW1’: {‘IP’: ‘10.1.1.22’,
‘adjacent_devices’: [‘R1’, ‘R2’, ‘R3’, ‘R4’, ‘R5’],
‘device_type’: ‘Switch’,
‘model’: ‘WS-C2950-24’,
‘vendor’: ‘cisco’}}

Video Archive

Week1
Introduction and Some Questions
What is the Nature of Python
Interpreter Shell, Variables, and Assignment
Strings

Week2
Introduction
Print and raw_input
Numbers
Lists and Tuples
Booleans

Week3
Introduction
If Conditionals
For Loops
Passing Arguments into a Script

Week4
Introduction
While Loops
Dictionaries
Exceptions

Reference

Kirk Byers
https://pynet.twb-tech.com
Twitter: @kirkbyers