Abstraction

In the previous sections, we learned how to create a new ops Feature. However, we have not yet discussed the concept of abstraction.

Before beginning this section, please review the pyats abstract_; particularly the part about Lookup class as this is the core of abstraction in Genie ops.

Strategy

There are primarily two reasons users rely on abstraction:

1. Device platform abstraction (Could be per OS type, or OS/Platform, etc.); and

2. Management interface abstract.

The abstraction package and Genie ops make both of these easy for users to achieve. Following the already defined directory Code Structure, abstraction determines which library to call depending on specific tokens.

Here is an example demonstrating what a section of the genie_libs directory looks like:

genie_libs
   `-- ops
       |-- __init__.py
       |-- tests
       |   `-- ospf -> ../ospf/tests
       `-- ospf
           |-- __init__.py
           |-- iosxe
           |   |-- __init__.py
           |   |-- ospf.py
           |   `-- yang
           |       |-- __init__.py
           |       `-- ospf.py
           |-- nxos
           |   |-- __init__.py
           |   |-- ospf.py
           |   `-- yang
           |       |-- __init__.py
           |       `-- ospf.py
           |-- iosxr
           |   |-- __init__.py
           |   |-- ospf.py
           |   `-- yang
           |       |-- __init__.py
           |       `-- ospf.py
           `-- tests
               |-- __init__.py
               `-- test_ospf.py

In this directory example, we have only given one level of OS abstraction, but additional tokens may be given, if required. Then we have our Yang directory abstraction.

Let’s go through the Yang Feature implementation:

The Cli and Yang structure must be the same. This is achieve with Metaparser which requires a schema, which is the same schema for Cli and Yang. This means the code in Ospf Cli implementation is also valid for Yang implementation; metaparser will return the same structure. Whenever the users calls metaparser, he or she must use the Yang function instead of Cli.

Additionally, Genie supports a hybrid model. In this hybrid model, some commands are sent via Cli and others are sent via Yang. This model is possible because of the self.context_manager, which specifies which function to call in metaparser, either cli, yang rest, or xml.

Let’s take a look at the nxos Ospf implementation for Yang:

from genie.libs.ops.ospf.nxos.ospf import Ospf as b_ospf
from genie.libs.ops.ops.base import Context
from genie.libs.parser.nxos import show_ospf

class Ospf(b_ospf):
    '''Ospf Ops Object'''

    # To keep short names
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.context_manager[show_ospf.ShowIpOspfVrfAll] = Context.yang
        self.context_manager[show_ospf.ShowIpOspfInterfaceVrfAll] = Context.yang
        self.context_manager[show_ospf.ShowIpOspfDatabase] = Context.Cli
        self.context_manager[show_ospf.ShowIpOspfNeighborsDetailVrfAll] = Context.yang

We want to use Yang for all commands, except for ShowIpOspfDatabase, which uses the Cli command. If the command does not exist in the context_manager, it will use Cli as the default.