[DAY#6 PyATS Series] Using pyATS CLI Tools: pyats learn, pyats parse – Vendor-Agnostic for Cisco, Arista, Palo Alto, FortiGate [Python for Network Engineer]

Introduction: Your First Step into CLI Magic with pyATS

Today’s blog is all about unlocking the CLI power of pyATS, specifically:

• pyats learn – Automatically discover your device state
• pyats parse – Convert CLI outputs into JSON for automation logic

These tools are a goldmine for Python for Network Engineer workflows, especially when working across vendors like Cisco, Arista, Palo Alto, and FortiGate.

By the end of this article, you’ll be able to:

• Connect to multi-vendor devices using testbed
• Learn and parse device states
• Integrate CLI parsing into your automation pipelines

Let’s jump in.

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Topology Overview

Here’s the setup we’re working with:

Each device is reachable over SSH via its management IP address. The pyATS runner machine initiates all interactions using Unicon and the pyats CLI.

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Why Vendor‑Agnostic Testing Matters

Networks today aren’t purely Cisco anymore. Most enterprise and cloud architectures include Arista for DC switching, FortiGate or Palo Alto for firewalls, and Cisco for routing/access.

Here’s how vendor-agnostic automation tools like pyATS change the game:

Problem	With pyATS CLI Tools
Inconsistent device outputs	Structured JSON from parse
Time-consuming manual validation	Auto-learn config/state using learn
Separate scripts per vendor	Unified CLI abstraction layer
Difficulty in comparing configs	Use diff with learn snapshots
Risk of human error	Repeatable CLI workflows

Using pyats learn and pyats parse, you get programmable CLI intelligence—something legacy tools can’t offer.

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Topology & Communications

Make sure your devices meet these basic requirements before proceeding:

Device	Vendor	IP Address	SSH Access	Required OS
R1	Cisco IOS	10.0.0.11	Yes	IOSv
SW1	Arista EOS	10.0.0.12	Yes	vEOS
PA1	Palo Alto	10.0.0.13	Yes	PAN-OS (CLI enabled)
FG1	FortiGate	10.0.0.14	Yes	FortiOS

Ensure:

• SSH/CLI is enabled
• Admin credentials are set
• pyATS can reach all hosts from your runner

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Workflow: pyATS CLI Commands in Action

Step 1: Test Connectivity

pyats validate testbed testbed.yml

Step 2: Learn Device State

pyats learn interface --testbed-file testbed.yml --devices R1

This will collect all interface data from R1 and store it under ./snapshots.

Step 3: Parse CLI Output

pyats parse "show version" --testbed-file testbed.yml --devices R1

This parses the raw CLI output and returns a structured JSON object.

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Explanation by Line

Here’s what’s happening behind the scenes for each command:

1. pyats validate testbed

• Ensures your YAML is syntactically correct.
• Checks device reachability and credentials.

2. pyats learn <feature>

• Runs predefined parsers for a given feature (like interface, routing, etc.)
• Saves results in a JSON file
• Works across supported vendors (limited features for Palo/Forti)

3. pyats parse "<command>"

• Runs the specified command on the target device
• Uses Genie parsers to structure output
• Helps in extracting key-value data from legacy CLI

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testbed.yml Example

testbed:
  name: MultiVendorLab
  credentials:
    default:
      username: admin
      password: password123

devices:
  R1:
    os: ios
    type: router
    connections:
      defaults:
        class: unicon.Unicon
      cli:
        protocol: ssh
        ip: 10.0.0.11

  SW1:
    os: eos
    type: switch
    connections:
      defaults:
        class: unicon.Unicon
      cli:
        protocol: ssh
        ip: 10.0.0.12

  PA1:
    os: panos
    type: firewall
    connections:
      defaults:
        class: unicon.Unicon
      cli:
        protocol: ssh
        ip: 10.0.0.13

  FG1:
    os: fortinet
    type: firewall
    connections:
      defaults:
        class: unicon.Unicon
      cli:
        protocol: ssh
        ip: 10.0.0.14

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Multi‑Vendor CLI Screenshots

Cisco (show version parsed)

{
  "version": {
    "version_short": "15.6",
    "platform": "IOSv",
    "hostname": "R1"
  }
}

Arista (show interfaces)

{
  "Ethernet1": {
    "oper_status": "up",
    "mtu": 1500
  }
}

Palo Alto / FortiGate

# No built-in parsers for most CLI, but connection via pyATS is working
# Can use custom parsers or external JSON logic

For Palo and Forti, you can still automate CLI collection and parse manually or with custom Python functions.

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FAQs

1. What is the difference between learn and parse in pyATS?

Answer:

• learn discovers full feature states using multiple commands (like all interfaces).
• parse runs a single command and parses its output to JSON.

2. Can I use parse with FortiGate or Palo Alto?

Answer:
Native Genie parsers are limited. You’ll likely need custom parsing logic using regex or TextFSM for unsupported vendors.

3. How to diff two snapshots using pyATS?

Answer:

pyats diff snapshots/R1/initial snapshots/R1/modified

This helps track config or state drift between two time points.

4. Is this usable in CI/CD pipelines?

Answer:
Yes! All pyats CLI tools are CLI-native and can be integrated into Jenkins, GitHub Actions, or GitLab pipelines.

5. How does pyATS handle login issues or SSH timeout?

Answer:
It raises Unicon exceptions, which are caught in CLI logs. Always validate testbed and use proper os, type, and ip.

6. What features are supported under learn?

Answer:
Common ones: interface, routing, platform, ospf, bgp, lldp, etc. Vendor support varies—best with Cisco and Arista.

7. Can I export parsed output to a file?

Answer:
Yes:

pyats parse "show version" --testbed-file testbed.yml --devices R1 > output.json

8. Is Genie still required separately?

Answer:
Genie is integrated into pyATS 23+. You don’t need separate installs unless using legacy APIs.

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YouTube Link

Watch the Complete Python for Network Engineer: Using pyATS CLI Tools: pyats learn, pyats parse – Vendor-Agnostic for Cisco, Arista, Palo Alto, FortiGate Lab Demo & Explanation on our channel:

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Join Our Training Program

If you’re enjoying these hands-on CLI workflows, it’s time to take it to the next level.

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• Python for Network Engineer automation
• Ansible + REST APIs
• Cisco DevNet Blueprints
• pyATS – from beginner to production

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Course Outline:
https://course.networkjourney.com/python-ansible-api-cisco-devnet-for-network-engineers/

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