Alexey (Oleksii) BorisenkoDevNet deloper advocate@alex_dev_k

DEVWKS-1512

Using YAML and Jinja Templates to Create Reusable Code

Becoming the Jinja Ninja

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• Introduction

• Reading YAML Formatted Data

• Working with Jinja Templates

• Pulling it All Together

• Wrap-Up

Agenda

DEVWKS-1512

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The Foundation for Reusable Code

• Scripting Language• Ex: Python, Ansible, NSO

• Templates – Sets of re-usable configuration and operational command sets. Include logic for substitution of device specific parameters • Ex: Jinja2, TextFSM, Notepad J

• Structured Data – Any data that exists in a fixed field within a record or a file• Ex: Dictionaries, Lists, CSV, YAML

DEVWKS-1512

A Brief Primer on YAML

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A human readable data structure that

applications use to store, transfer, and read data.

YAML - “YAML Ain’t Markup Language”

DEVWKS-1512

---ietf-interfaces:interface:name: GigabitEthernet2description: Wide Area Networkenabled: trueietf-ip:ipv4:address:- ip: 172.16.0.2netmask: 255.255.255.0

Jinja Templating

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• Jinja2 is one of the most used template engines for Python.

• Extends capabilities through tools such as loops, conditionals and inheritance.

• Installed via pip

• http://jinja.pocoo.org

Jinja Templating

DEVWKS-1512

{% for member in band_member -%}

{% if member.instrument == "Singer" -%}{{ member.name }} Ramone is the{{ member.instrument }}

{% else -%}{{ member.name }} Ramone plays the{{ member.instrument }}

{% endif -%}

{% endfor -%}

Jinja Templating – Loops and Conditionals

Johnny, GuitarDee Dee, Bass Joey, SingerTommy, Drums

Johnny Ramone plays the GuitarDee Dee Ramone plays the BassJoey Ramone is the SingerTommy Ramone plays the Drums

Input: Output:

• Variables and/or logic are placed between delimiters• {% …. %} - Used for expressions or loops.

• ‘-%}’ – Removes additional white space.

• {{ …. }} – Used for outputting the expression or variable.

• Loops• Opened with {% for ‘x’ in ‘y’ %} and typically fed in

from some form of programmatic script.• Closed with {% endfor %}

• Conditionals• Can be nested in other operations• if, elif, else otpions (ex: {% if x == y %}• Closed with {% endif %}

{% for input in inputs -%}

{% if input.name == "Tyrion" -%}

"{{ input.motto }}" motto of {{ input.house }}

{% elif input.name == "Jon Snow" -%}

"{{ input.motto }}" motto of {{ input.house }}

{% else -%}

"{{ input.motto }}" motto of {{ input.house }}

{% endif -%}

{% endfor -%}

Jinja Templating – Loops and Conditionals

"Hear Me Roar!, A Lannister Always Pays His Debts" motto of House Lannister"Winter Is Coming" motto of House Stark"Fire And Blood" motto of House Targaryen

Output:

• Variables and/or logic are placed between delimiters• {% …. %} - Used for expressions or loops.

• ‘-%}’ – Removes additional white space.

• {{ …. }} – Used for outputting the expression or variable.

• Loops• Opened with {% for ‘x’ in ‘y’ %} and typically fed in

from some form of programmatic script.• Closed with {% endfor %}

• Conditionals• Can be nested in other operations• if, elif, else otpions (ex: {% if x == y %}• Closed with {% endif %}

Workshop repohttps://github.com/oborys/DEVWKS-1512

Wrap Up!

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