Managed Attribute¶
managedattribute allows finer controls on how attributes are created, while
taking care of mundane and repetitive actions :
Automatically document your code (provided the
docargument is used)Restricts value of the variables to be of certain types (makes the code more resistant)
Mechanism to set variable to be read-only
Defaults value for the variable
…
Let’s play with some examples. It is highly encouraged to try it in your own terminal and experience it yourself.
from genie.decorator import managedattribute
class Test(object):
# Create pid attribute
pid = managedattribute(
name='pid',
doc='Pid of some application')
# Create a name, which is read-only
name = managedattribute(
name='name',
read_only=True,
doc='Name of some application')
# Create speed with a default of 1000
# and the type of the value must be an int
speed = managedattribute(
name='speed',
default=1000,
type=managedattribute.test_istype(int),
doc='Speed of the application')
test = Test()
# Let's test pid
# It behaves exactly the same as a normal attribute
test.pid = 5
print(test.pid)
# 5
test.pid = 9
print(test.pid)
# 9
# Read-only attribute. It cannot be modified via the
# attribute name itself. It has to be done via _attribute
test.name = 'myApp'
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# File ".../genie/src/genie/decorator.py", line 714, in __set__
# raise AttributeError('can\'t set attribute')
# AttributeError: can't set attribute
# Now it can be modified via the _name
test._name = 'myApp'
print(test.name)
# myApp
test.speed
# 1000
test.speed = 'not an int'
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# File ".../genie/src/genie/decorator.py", line 718, in __set__
# return fset(inst, value)
# File ".../genie/src/genie/decorator.py", line 512, in _default_setter
# value = self._transform(value, self.__type)
# File ".../genie/src/genie/decorator.py", line 477, in _transform
# raise ValueError('{}: {}'.format(value, ' '.join(exceptions)))
# ValueError: not an int: Not of type int.
test.speed = 9
test.speed
# 9
# Finally, automatic documentation
help(Test)
Hint
All code in those examples are executable. This allows you to play with the code as you read.
Hint
To execute those example, source your virtual environment, type python, and paste the code in there.
Important details about managedattribute.
namehas to be exactly the same as the variable name.Read-onlyattributes cannot be modified, however it can be modified by adding a_in front of the variable name. This assure that it wouldn’t be modified by mistake, but always on purpose. (Look at thenameexample)Many type can be given via tuple; for example:
type=(None, managedattribute.test_is(False), managedattribute.test_istype(str),).
Let’s re-write our previous example with manageattribute.
#### Imports ####
from genie.conf import Genie
from genie.conf.base import Device
from genie.conf.base import Testbed
from genie.decorator import managedattribute
from genie.conf.base.config import CliConfig
from genie.conf.base.base import DeviceFeature
from genie.conf.base.cli import CliConfigBuilder
from genie.conf.base.attributes import DeviceSubAttributes,\
SubAttributesDict,\
AttributesHelper
#### Vrf class ####
class Vrf(DeviceFeature):
class DeviceAttributes(DeviceSubAttributes):
def build_config(self, devices=None, apply=True, attributes=None,
unconfig=False):
# List containing configuration for this loop
# Instantiate configurations
configurations = CliConfigBuilder(unconfig=unconfig)
# Create Vrf Submode context
with configurations.submode_context(
attributes.format('vrf {name}',
force=True)):
if unconfig and attributes.iswildcard:
configurations.submode_unconfig()
configurations.append_line(attributes.format('description {description}'))
configurations.append_line(attributes.format('rd {rd}'))
return CliConfig(device=self.device, unconfig=unconfig,
cli_config=configurations)
# Create the subAttributesDict for device_att
# We want it readonly, as the dict shouldn't never be changed,
# only the key/value.
device_attr = managedattribute(
name='device_attr',
read_only=True,
doc=DeviceAttributes.__doc__)
# When the variable is first created, it creates a subAttributesDict
@device_attr.initter
def device_attr(self):
return SubAttributesDict(self.DeviceAttributes, parent=self)
# __init__ of Vrf
name = managedattribute(
name='name',
read_only=True,
doc='Name of the Vrf')
description = managedattribute(
name='description',
type=managedattribute.test_istype(str),
doc='Description of the Vrf')
rd = managedattribute(
name='rd',
type=managedattribute.test_istype(str),
doc='Rd of the Vrf')
def __init__(self, name, *args, **kwargs):
self._name = name
super().__init__(*args, **kwargs)
# Adding a new build_config, to call
def build_config(self, devices=None, apply=True, attributes=None,
unconfig=False):
cfgs = {}
attributes = AttributesHelper(self, attributes)
if devices is None:
devices = self.devices
devices = set(dev.name for dev in devices)
# Loop over all the items of 'self.device_attr', sort them,
# and only care about the keys which are in keys.
for key, sub, attributes2 in attributes.mapping_items(
'device_attr', keys=devices, sort=True):
# For each, call their build_config with attributes as an argument.
# attributes2 is only the attributes related to this particular
# device, and its parent attributes. (To allow parent default
# values)
cfgs[key] = sub.build_config(apply=False,
attributes=attributes2,
unconfig=unconfig)
if apply:
for device_name, cfg in sorted(cfgs.items()):
if cfg:
device = self.testbed.devices[device_name]
device.configure(cfg)
else:
return cfgs
#### Main section ####
# Set Genie Tb
testbed = Testbed()
Genie.testbed = testbed
dev1 = Device(name='pe1', testbed=testbed, os='nxos')
dev2 = Device(name='pe2', testbed=testbed, os='nxos')
vrf1 = Vrf(name='blue')
# Let's add a specific description, and a default one
vrf1.device_attr[dev1.name].description = 'Pe1 blue vrf'
vrf1.description = 'Default description'
# And same RD for both, we can set it at the parent level as we want it
# to be of the same value
vrf1.rd = '800:1'
print(vrf1.build_config(devices=[dev1, dev2], apply=False))
# {'pe2': 'vrf blue\n description Default description\n rd 800:1\n exit',
# 'pe1': 'vrf blue\n description Pe1 blue vrf\n rd 800:1\n exit'}
help(Vrf)
We’ve seen the following arguments :
name : Must match the name of the variable
default : Default value for this variable
read_only : The variable cannot be written to, except using
_in front of it it also cannot have a type.doc : Set documentation
The use of
initterto initialize class for usingSubAttributesDict