Anatomy of a Python Script

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).