---
title: "Anatomy of a Python Script"
canonical: "https://docs.infoblox.com/space/NetMRI753/41944949/Anatomy%20of%20a%20Python%20Script"
format: markdown
---
> ⚠️ **Note**
> ⚠️ 
> ⚠️ Well-known variables for Python scripting are listed in the topic *<span style="color: #0000ff">[Scripting](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>*[ ](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)*<span style="color: #0000ff">[Well-Known](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>*[ ](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)*<span style="color: #0000ff">[Variables](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>*[ ](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)*<span style="color: #0000ff">[(Perl, Python, ](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>**<span style="color: #0000ff">[and](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>*[ ](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)*<span style="color: #0000ff">[CCS)](https://infoblox-docs.atlassian.net/wiki/spaces/NetMRI753/pages/42403211)</span>*.

Python scripts use a script header similar to a CCS script, contained within a well-known comment block.

The script header block influences a number of runtime behaviors, including:

**Script-Timeout**

Specifies the per-command timeout for the entire script in seconds.

- Type: Integer
- Required: No
- Default if not specified: 60

**Script-Login**

Specifies whether the job engine should automatically establish a connection with the target device.

- Type: Boolean
- Required: No
- Default if not specified: true

**Script-Variables**

- Specifies inputs needed by the script.
- Type: Tuple (ordered list of elements)
- Required: No
- Default if not specified: None

**Script-Filter**

Specifies the device types processed by the script.

- Type: String
- Required: Yes

A Python Script header block must be defined inside of comments within a "well known" comment section (between # BEGIN-SCRIPT-BLOCK and a # END-SCRIPT-BLOCK). The following example demonstrates the difference between a CCS and Python Script header block that specifies a Script-Filter that applies to all Cisco IOS devices.

As a comparison, a CCS implementation is straightforward:

`Script-Filter: $Vendor == "Cisco" and $sysDesc like /IOS/`

You can filter by the network view:

`Script-Filter: $network == "blue"`

A comparable Python implementation is as follows:

`# BEGIN-SCRIPT-BLOCK`

`# Script-Filter: $Vendor == "Cisco" and $sysDesc like /IOS/`

`# END-SCRIPT-BLOCK`

Python scripts run inside the sandbox, using the Pyrthon API to communicate with the Device Interaction Server (DIS) on NetMRI. The DIS proxies CLI requests/responses to/from network devices on behalf of the Python scripts. Before commands can be sent to a network device, a Python script must first establish a DIS session (see v2 API object DisSession). After a session has been established, a CLI connection with the target device must be established for the given session (see v2 API object CliConnection). The majority of the time, a Python script will follow this same initialization sequence. First, establish the API session, establish the DIS session, then establish a CLI connection with the target device. For this reason, netmri_easy.py, a pre-installed Python library, is provided in the appliance (see **Configuration Management **>** Job Management **>** Library **>** netmri_easy**).