Examples¶
This section provides an example on how to create a parser class based on
metaparser. A working example show_version can be found under
parser directory: parser/nxos/show_version.py for future
reference.
What parser to write?¶
Find the equivalent cli which matches the parsing purpose. Let’s give an example: write a nxos xml parser for ‘show ipv4 ospf neighbor’.
Check the parser existence¶
Before starting, it is always recommended to check whether the desired parser
already exists under parser directory, or use the GROC tool to
search.
Requirement to name a parser module (parser file): Module name (file name) should be the first two words of the corresponding cli command or equivalent. If the first two words contain strong ambiguity (e.g.: show ip), extend the next word to clarify the parser purpose.
Therefore, looking for file “show_ipv4_ospf.py” under directory
parser/nxos.
If the parser module does not exist, developer has to create a new parser module which contains the desired parser - see Create a Parser Module for detail.
However, if the parser module looks promising based on the file name, open the file and check if it contains the parser class implementation.
Requirement to name a parser class: We strongly recommend to name the class using the full cli command or equivalent to represent the actual parser. For variable phrases within the parser class name (e.g.: show interface Eth3/4), use _WORD_ to present the phrase (e.g.: ShowInterface_WORD_).
Therefore, looking for class ShowIpv4OspfNeighbor within module
show_ipv4_ospf.py.
If no class is present, developer has to create the parser class - see Create a Parser Class for detail.
In case of the parser class has been defined, look into class to further check if the desired parsing mechanism - xml() has also been implemented.
If xml() function has been defined, and the output structure fulfills the
developer’s expectation - Great! If the parsing output structure does not
satisfy developer’s needs, object-orientation inheritance concept will be
applied here. However, if the parsing mechanism xm() has not been defined,
developer has to write the parsing method - see Implement Parsing Mechanisms
for detail.
Create a parser module¶
Parser file contains at least one parser class which includes actual parsing mechanisms (cli, xml, yang) implementation. All relevant parser classes (name with same starting words) should be colocated in the same file. For instance, parser class ShowXxx, ShowXxxYyy, and ShowXxxYyyZzz should be implemented in file: show_xxx.py.
Example: create a new file named show_ipv4_ospf.py under nxos directory
Create a parser class¶
Example: create parser class named ShowIpv4OspfNeighbor in parser file
show_ipv4_ospf.py.
Define the parser output schema for this class. The purpose is to make sure the parser always returns the output (nested dict) that has the same data structure across all supported parsing mechanisms (cli(), yang(), xml()).
# module show_ipv4_ospf.py
# ------------------------
# import packages need to use in this module
from genie.metaparser import MetaParser
from genie.metaparser.util.schemaengine import Any
# define parser class
class ShowIpv4OspfNeighbor(MetaParser):
# define scheme here, Any() in schema acting like a wildcard character,
# usually used to presenting the variable keys within the dictionary.
# For more info on how to define a schema: please read schemaengine API
# doc.
schema = {'intf': {
Any(): {
'neighbor': str,
'interface_address': str,
'process_id': str,
'vrf': str,
'area': str,
'state': str,
'dr': str,
'bdr': str,},},
'intf_list': str,}
Implement parsing mechanisms¶
Current parser infra supports ‘cli’, ‘xml’, and ‘yang’ as its parsing mechanisms. Each parsing mechanism will be implemented as a Python method within the parser class.
Example: implement class method xml().
Function xml() defines the xml type output parsing mechanism which typically contains 3 steps: executing, transforming, and returning.
Step1 - executing
Developer has choices of calling the existing xml parsers from known libraries, or implementing new parsing mechanism here.
Step2 - transforming
This step might be optional for the first parser mechanism writer. The purpose of this step is to enforce the final output structure from all different parsing mechanisms (cli(), xml(), yang()) to be same. Developer can greatly leverage all the functionalities provided in
metaparser.utilclass.Useful tools to do the transformation: dict.update() –> adding missing key-value pairs metaparser.util.keynames_convert() –> nested key names converting
Step3: - returning
Returns the final result - the structure of the result has to be (nested)dictionary.
For detail example, please read Template Documentation, and reference the example:
parser/nxos/show_platform.py.
def xml(self):
out = self.device.execute('show ipv4 ospf neighbor | xml')
etree_dict = {}
# Remove junk characters returned by the device
out = out.replace("]]>]]>", "")
output = ET.fromstring(out)
for item in output:
for data in item:
for show in data:
for ospf in show:
for __XML__OPT_Cmd_show_ip_ospf_session_cmd_vrf in ospf:
for process in __XML__OPT_Cmd_show_ip_ospf_session_cmd_vrf:
for __XML__OPT_Cmd_show_ospf_process_cmd_vrf in process:
for __XML__OPT_Cmd_show_ospf_process_cmd___readonly__ in __XML__OPT_Cmd_show_ospf_process_cmd_vrf:
for key in __XML__OPT_Cmd_show_ospf_process_cmd___readonly__:
# Get key text
text = key.tag[key.tag.find('}')+1:]
# ospf_pid
if text == 'processid':
etree_dict['ospf_pid'] = int(key.text)
# ospf_protocol_started_reason
if text == 'protocolstartedreason':
etree_dict['ospf_protocol_started_reason'] = key.text
# ospf_tag
if text == 'protocoltag':
etree_dict['ospf_tag'] = key.text
# ospf_protocol_state
if text == 'protocolstate':
etree_dict['ospf_protocol_state'] = str(key.text).lower()
# ospf_isolate_mode
if text == 'isolatemode':
etree_dict['ospf_isolate_mode'] = key.text
# ospf_mmode
if text == 'mmode':
etree_dict['ospf_mmode'] = key.text
# ospf_memory_state
if text == 'memorystate':
etree_dict['ospf_memory_state'] = str(key.text).lower()
# ospf_performance_mode
if text == 'forwardingstatesaved':
if key.text == 'false':
etree_dict['ospf_performance_mode'] = 'No'
else:
etree_dict['ospf_performance_mode'] = 'Yes'
# ospf_asformat
if text == 'asformat':
etree_dict['ospf_asformat'] = key.text
if text == 'srgbmin':
srgbin = key.text
if text == 'srgbmax':
srgmax = key.text
try:
etree_dict['segment_routing_global_block'] = srgbin + '-' + srgmax
except Exception:
pass
# num_attr_entries
if text == 'attributeentries':
etree_dict['num_attr_entries'] = int(key.text)
# hwm_attr_entries
if text == 'hwmattributeentries':
etree_dict['hwm_attr_entries'] = int(key.text)
# bytes_used
if text == 'bytesused':
etree_dict['bytes_used'] = int(key.text)
# entries_pending_delete
if text == 'entriespendingdelete':
etree_dict['entries_pending_delete'] = int(key.text)
# hwm_entries_pending_delete
if text == 'hwmentriespendingdelete':
etree_dict['hwm_entries_pending_delete'] = int(key.text)
# ospf_paths_per_hwm_attr
if text == 'pathsperattribute':
etree_dict['ospf_paths_per_hwm_attr'] = int(key.text)
# ospf_as_path_entries
if text == 'aspathentries':
etree_dict['ospf_as_path_entries'] = int(key.text)
# bytes_used_as_path_entries
if text == 'aspathbytes':
etree_dict['bytes_used_as_path_entries'] = int(key.text)
if text == 'TABLE_vrf':
for table_vrf in key:
for row_vrf in table_vrf:
vrf_tag = row_vrf.tag[row_vrf.tag.find('}')+1:]
# vrf
# vrf_name
if vrf_tag == 'vrf-name-out':
vrf_name = row_vrf.text
if 'vrf' not in etree_dict:
etree_dict['vrf'] = {}
if vrf_name not in etree_dict['vrf']:
etree_dict['vrf'][vrf_name] = {}
vrf_dict = etree_dict['vrf'][vrf_name]
# vrf_id
if vrf_tag == 'vrf-id':
vrf_dict['vrf_id'] = row_vrf.text
# vrf_state
if vrf_tag == 'vrf-state':
vrf_dict['vrf_state'] = str(row_vrf.text).lower()
# router_id
if vrf_tag == 'vrf-router-id':
vrf_dict['router_id'] = row_vrf.text
# conf_router_id
if vrf_tag == 'vrf-cfgd-id':
vrf_dict['conf_router_id'] = row_vrf.text
# confed_id
if vrf_tag == 'vrf-confed-id':
vrf_dict['confed_id'] = int(row_vrf.text)
# cluster_id
if vrf_tag == 'vrf-cluster-id':
vrf_dict['cluster_id'] = row_vrf.text
# num_conf_peers
if vrf_tag == 'vrf-peers':
vrf_dict['num_conf_peers'] = int(row_vrf.text)
# num_pending_conf_peers
if vrf_tag == 'vrf-pending-peers':
vrf_dict['num_pending_conf_peers'] = int(row_vrf.text)
# num_established_peers
if vrf_tag == 'vrf-est-peers':
vrf_dict['num_established_peers'] = int(row_vrf.text)
vrf_dict['vrf_rd'] = 'not configured'
# vrf_rd
if vrf_tag == 'vrf-rd':
vrf_dict['vrf_rd'] = row_vrf.text
if vrf_tag == 'TABLE_af':
for table_af in row_vrf:
for row_af in table_af:
af_tag = row_af.tag[row_af.tag.find('}')+1:]
# address_family
# address_family_name
if af_tag == 'af-name':
address_family_name = str(row_af.text).lower()
if 'address_family' not in etree_dict['vrf'][vrf_name]:
etree_dict['vrf'][vrf_name]['address_family'] = {}
if address_family_name not in etree_dict['vrf'][vrf_name]['address_family']:
etree_dict['vrf'][vrf_name]['address_family'][address_family_name] = {}
af_dict = etree_dict['vrf'][vrf_name]['address_family'][address_family_name]
# Initialize empty lists
export_rt_list = ''
import_rt_list = ''
# table_id
if af_tag == 'af-table-id':
table_id = str(row_af.text)
if '0x' in table_id:
af_dict['table_id'] = table_id
else:
af_dict['table_id'] = '0x' + table_id
# table_state
if af_tag == 'af-state':
af_dict['table_state'] = str(row_af.text).lower()
# peers
if af_tag == 'af-num-peers':
peers = int(row_af.text)
if 'peers' not in af_dict:
af_dict['peers'] = {}
if peers not in af_dict['peers']:
af_dict['peers'][peers] = {}
# active_peers
if af_tag == 'af-num-active-peers':
af_dict['peers'][peers]['active_peers'] = int(row_af.text)
# routes
if af_tag == 'af-peer-routes':
af_dict['peers'][peers]['routes'] = int(row_af.text)
# paths
if af_tag == 'af-peer-paths':
af_dict['peers'][peers]['paths'] = int(row_af.text)
# networks
if af_tag == 'af-peer-networks':
af_dict['peers'][peers]['networks'] = int(row_af.text)
# aggregates
if af_tag == 'af-peer-aggregates':
af_dict['peers'][peers]['aggregates'] = int(row_af.text)
# route_reflector
if af_tag == 'af-rr':
if row_af.text == 'true':
af_dict['route_reflector'] = True
# next_hop_trigger_delay
# critical
if af_tag == 'nexthop-trigger-delay-critical':
if 'next_hop_trigger_delay' not in af_dict:
af_dict['next_hop_trigger_delay'] = {}
af_dict['next_hop_trigger_delay']['critical'] = int(row_af.text)
# next_hop_trigger_delay
# non_critical
if af_tag == 'nexthop-trigger-delay-non-critical':
af_dict['next_hop_trigger_delay']['non_critical'] = int(row_af.text)
# aggregate_label
if af_tag == 'af-aggregate-label':
af_dict['aggregate_label'] = row_af.text
# label_mode
if af_tag == 'af-label-mode':
af_dict['label_mode'] = row_af.text
# import_default_map
if af_tag == 'importdefault_map':
af_dict['import_default_map'] = row_af.text
# import_default_prefix_limit
if af_tag == 'importdefault_prefixlimit':
af_dict['import_default_prefix_limit'] = int(row_af.text)
# import_default_prefix_count
if af_tag == 'importdefault_prefixcount':
af_dict['import_default_prefix_count'] = int(row_af.text)
# export_default_map
if af_tag == 'exportdefault_map':
af_dict['export_default_map'] = row_af.text
# export_default_prefix_limit
if af_tag == 'exportdefault_prefixlimit':
af_dict['export_default_prefix_limit'] = int(row_af.text)
# export_default_prefix_count
if af_tag == 'exportdefault_prefixcount':
af_dict['export_default_prefix_count'] = int(row_af.text)
# TABLE_redist
# ROW_redist
if af_tag == 'TABLE_redist':
for table_redist in row_af:
for row_redist in table_redist:
row_redist_tag = row_redist.tag[row_redist.tag.find('}')+1:]
# protocol
if row_redist_tag == 'protocol':
protocol = row_redist.text
if 'redistribution' not in af_dict:
af_dict['redistribution'] = {}
if protocol not in af_dict['redistribution']:
af_dict['redistribution'][protocol] = {}
# route_map
if row_redist_tag == 'route-map':
af_dict['redistribution'][protocol]['route_map'] = row_redist.text
# TABLE_evpn_export_rt
# ROW_evpn_export_rt
if af_tag == 'TABLE_evpn_export_rt':
for table_evpn_export in row_af:
for row_export in table_evpn_export:
row_export_tag = row_export.tag[row_export.tag.find('}')+1:]
# export_rt_list
if row_export_tag == 'evpn-export-rt':
export_rt_list = str(export_rt_list + ' ' + row_export.text).strip()
af_dict['export_rt_list'] = export_rt_list
# TABLE_evpn_import_rt
# ROW_evpn_import_rt
if af_tag == 'TABLE_evpn_import_rt':
for table_evpn_import in row_af:
for row_import in table_evpn_import:
row_import_tag = row_import.tag[row_import.tag.find('}')+1:]
# export_rt_list
if row_import_tag == 'evpn-import-rt':
import_rt_list = str(import_rt_list + ' ' + row_import.text).strip()
af_dict['import_rt_list'] = import_rt_list
# parsed all tags
continue
return etree_dict
XML Parser Using ETree¶
Please refer to this file for an example XML Parser Using Regular Expressions
XML Parser Using Regular Expressions¶
Please refer to this file for an example XML Parser Using ETree